Credit students for cancelled paid lessons

Cancelling a lesson that was already paid for now credits the student
that money instead of leaving it as a manual refund, and the daily
scheduled-billing scan applies any available credit against their due
charges before emailing the notice.

- New us_credits ledger + us_payments.credit_applied column (Payment::netDue).
- PaymentService::creditForCancelledLesson issues a per-lesson share of the
  covering payment's total; wired into all three cancel paths (student
  self-cancel, instructor status update, admin student-detail cancel).
- PaymentService::applyCredits draws credit down FIFO across a run's charges,
  marking a fully-covered charge paid-by-credit; the notice shows the credit
  applied and reduced total, and the admin queue shows net due.
- Student detail page shows a student's credit balance and history.

Ships as part of the unreleased 1.2.0 (same release as scheduled billing).

Tests: composer test (585), composer lint, composer cs all pass.

Co-Authored-By: Claude Opus 4.8 <[email protected]>

src/AdminMenu.php

@@ -25,6 +25,7 @@ use Unsupervised\Schedular\Offering\ClassSlotReconciler;
 use Unsupervised\Schedular\Offering\OfferingController;
 use Unsupervised\Schedular\Offering\OfferingRepository;
 use Unsupervised\Schedular\Payment\BillingMethodResolver;
+use Unsupervised\Schedular\Payment\CreditRepository;
 use Unsupervised\Schedular\Payment\PaymentController;
 use Unsupervised\Schedular\Payment\PaymentReportController;
 use Unsupervised\Schedular\Payment\PaymentRepository;
@@ -56,7 +57,7 @@ class AdminMenu {
 	private PaymentController $paymentController;
 	private PaymentReportController $paymentReportController;
 
-	public function __construct( AvailabilityRepository $availability, BookingRepository $bookings, OfferingRepository $offerings, QuestionRepository $questions, AnswerRepository $answers, PolicyRepository $policies, PolicyVersionRepository $policyVersions, PolicyService $policyService, AcceptanceRepository $acceptances, InviteRepository $invites, EnrollmentRepository $enrollments, GroupAccessRepository $groupAccess, StudioSettings $settings, PaymentRepository $payments, PaymentService $paymentService, BillingMethodResolver $resolver, RegistrationMailer $registrationMailer ) {
+	public function __construct( AvailabilityRepository $availability, BookingRepository $bookings, OfferingRepository $offerings, QuestionRepository $questions, AnswerRepository $answers, PolicyRepository $policies, PolicyVersionRepository $policyVersions, PolicyService $policyService, AcceptanceRepository $acceptances, InviteRepository $invites, EnrollmentRepository $enrollments, GroupAccessRepository $groupAccess, StudioSettings $settings, PaymentRepository $payments, PaymentService $paymentService, BillingMethodResolver $resolver, RegistrationMailer $registrationMailer, CreditRepository $credits ) {
 		$this->availabilityController         = new AvailabilityController( $availability, $offerings );
 		$this->lessonController               = new LessonController( $bookings, $payments, $availability, $offerings, new LessonDetail( $answers, $questions, $acceptances, $policies, $policyVersions ) );
 		$this->offeringController             = new OfferingController( $offerings, new ClassSlotReconciler( $availability ) );
@@ -65,7 +66,7 @@ class AdminMenu {
 		$this->registrationController         = new RegistrationController( $invites );
 		$this->registrationApprovalController = new RegistrationApprovalController( $registrationMailer );
 		$this->groupClassController           = new GroupClassController( $enrollments, $offerings, $payments, $groupAccess, $paymentService, $invites, $registrationMailer );
-		$this->studentController              = new StudentController( $bookings, $availability, $offerings, $enrollments, $resolver, new StudentHistory( $acceptances, $policies, $policyVersions, $answers, $questions, $payments ), new StudentActions( $bookings, $availability, $enrollments, $paymentService ) );
+		$this->studentController              = new StudentController( $bookings, $availability, $offerings, $enrollments, $resolver, new StudentHistory( $acceptances, $policies, $policyVersions, $answers, $questions, $payments, $credits ), new StudentActions( $bookings, $availability, $enrollments, $paymentService ) );
 		$this->instructorController           = new InstructorController();
 		$this->settings                       = $settings;
 		$this->accessSettings                 = new AccessSettings();

src/Auth/StudentActions.php

@@ -27,8 +27,9 @@ class StudentActions {
 
 	/**
 	 * Cancel a lesson on the student's behalf: marks it cancelled, frees the
-	 * slot for rebooking, and voids a still-pending payment. Paid lessons keep
-	 * their payment — refunds are a manual, admin-side decision.
+	 * slot for rebooking, and voids a still-pending payment. A paid lesson is
+	 * credited back to the student's account (a per-lesson share of what they
+	 * paid) to offset their future scheduled billing.
 	 */
 	public function cancelLesson( int $lessonId, int $studentId ): bool {
 		$lesson = $this->bookings->findById( $lessonId );
@@ -40,6 +41,7 @@ class StudentActions {
 		$this->bookings->updateStatus( $lessonId, Lesson::STATUS_CANCELLED );
 		$this->availability->release( $lesson->slotId );
 		$this->payments->voidPending( $lesson->paymentId );
+		$this->payments->creditForCancelledLesson( $lesson );
 
 		return true;
 	}

src/Auth/StudentController.php

@@ -149,11 +149,24 @@ class StudentController {
 		$registrationInfo = $this->history->registrationInfo( (int) $student->ID );
 		$intake           = $this->history->intakeAnswers( (int) $student->ID );
 		$payments         = $canBilling ? $this->history->payments( (int) $student->ID ) : [];
+		$credits          = $canBilling ? $this->history->credits( (int) $student->ID ) : [];
+		$creditBalance    = $canBilling ? $this->history->creditBalance( (int) $student->ID ) : 0.0;
+		$creditCurrency   = $this->creditCurrency( $credits );
 
 		$backUrl = admin_url( 'admin.php?page=us-students' );
 		include USC_PLUGIN_DIR . 'templates/admin/student-detail.php';
 	}
 
+	/**
+	 * Currency to label the credit balance with — taken from the student's credits
+	 * (they share a currency in practice), defaulting to CAD when they have none.
+	 *
+	 * @param list<array{created_at: string, amount: float, remaining: float, currency: string, reason: string, status: string}> $credits
+	 */
+	private function creditCurrency( array $credits ): string {
+		return [] !== $credits ? (string) $credits[0]['currency'] : 'CAD';
+	}
+
 	/**
 	 * Build a display row for a lesson (slot time, offering, instructor, status).
 	 *

src/Auth/StudentHistory.php

@@ -3,6 +3,8 @@ declare(strict_types=1);
 
 namespace Unsupervised\Schedular\Auth;
 
+use Unsupervised\Schedular\Payment\Credit;
+use Unsupervised\Schedular\Payment\CreditRepository;
 use Unsupervised\Schedular\Payment\Payment;
 use Unsupervised\Schedular\Payment\PaymentRepository;
 use Unsupervised\Schedular\Policy\AcceptanceRepository;
@@ -27,6 +29,7 @@ class StudentHistory {
 		private AnswerRepository $answers,
 		private QuestionRepository $questions,
 		private PaymentRepository $payments,
+		private CreditRepository $credits,
 	) {}
 
 	/**
@@ -129,6 +132,34 @@ class StudentHistory {
 		);
 	}
 
+	/**
+	 * The student's total unused credit balance (from cancelled paid lessons),
+	 * applied automatically against future scheduled-billing charges.
+	 */
+	public function creditBalance( int $studentId ): float {
+		return $this->credits->availableBalance( $studentId );
+	}
+
+	/**
+	 * Every credit the student has been issued, newest first, with the amount, what
+	 * remains, and its state.
+	 *
+	 * @return list<array{created_at: string, amount: float, remaining: float, currency: string, reason: string, status: string}>
+	 */
+	public function credits( int $studentId ): array {
+		return array_map(
+			static fn( Credit $credit ): array => [
+				'created_at' => $credit->createdAt ?? '',
+				'amount'     => $credit->amount,
+				'remaining'  => $credit->remaining,
+				'currency'   => $credit->currency,
+				'reason'     => $credit->reason ?? '—',
+				'status'     => $credit->status,
+			],
+			$this->credits->findByStudent( $studentId )
+		);
+	}
+
 	/**
 	 * Human label for a polymorphic registration target.
 	 */

src/Booking/BookingEndpoint.php

@@ -343,8 +343,9 @@ class BookingEndpoint {
 
 	/**
 	 * Student-initiated cancellation of their own lesson: marks it cancelled,
-	 * frees the slot for rebooking, and voids any still-pending payment. Paid
-	 * lessons keep their payment — refunds are a manual, admin-side decision.
+	 * frees the slot for rebooking, and voids any still-pending payment. A lesson
+	 * already paid for is credited back to the student's account (a per-lesson
+	 * share of the covering payment) to offset their future scheduled billing.
 	 */
 	public function cancel( \WP_REST_Request $request ): \WP_REST_Response|\WP_Error {
 		$id     = absint( Val::int( $request->get_param( 'id' ) ) );
@@ -379,6 +380,7 @@ class BookingEndpoint {
 			$this->bookings->updateStatus( $id, Lesson::STATUS_CANCELLED );
 			$this->availability->release( $lesson->slotId );
 			$this->payments->voidPending( $lesson->paymentId );
+			$this->payments->creditForCancelledLesson( $lesson );
 		}
 
 		return new \WP_REST_Response(
@@ -407,6 +409,7 @@ class BookingEndpoint {
 		if ( Lesson::STATUS_CANCELLED === $status && Lesson::STATUS_CANCELLED !== $lesson->status ) {
 			$this->availability->release( $lesson->slotId );
 			$this->payments->voidPending( $lesson->paymentId );
+			$this->payments->creditForCancelledLesson( $lesson );
 		} elseif ( Lesson::STATUS_CANCELLED === $lesson->status && Lesson::STATUS_CANCELLED !== $status && ! $this->availability->claim( $lesson->slotId ) ) {
 			// Reinstating a cancelled lesson must re-reserve its slot, and
 			// someone else may have booked the freed time in the meantime.

src/Booking/BookingRepository.php

@@ -243,6 +243,37 @@ class BookingRepository {
 		return $rows ?? [];
 	}
 
+	/**
+	 * How many lessons a payment covers — every lesson pointed at it, cancelled or
+	 * not, since the payment was billed for all of them. Used to split a paid
+	 * payment's total into a per-lesson share when one covered lesson is cancelled
+	 * and credited. Never below zero.
+	 */
+	public function countByPaymentId( int $paymentId ): int {
+		return (int) $this->db->get_var(
+			$this->db->prepare(
+				'SELECT COUNT(*) FROM %i WHERE payment_id = %d',
+				$this->table,
+				$paymentId
+			)
+		);
+	}
+
+	/**
+	 * How many lessons belong to a weekly series — the whole reservation an upfront
+	 * (full-term) payment covers, so cancelling one lesson credits its per-lesson
+	 * share. Counts every lesson in the series, cancelled or not.
+	 */
+	public function countBySeries( int $seriesId ): int {
+		return (int) $this->db->get_var(
+			$this->db->prepare(
+				'SELECT COUNT(*) FROM %i WHERE series_id = %d',
+				$this->table,
+				$seriesId
+			)
+		);
+	}
+
 	public function setPaymentId( int $id, int $paymentId ): bool {
 		return false !== $this->db->update(
 			$this->table,

src/Payment/Credit.php

@@ -0,0 +1,79 @@
+<?php
+declare(strict_types=1);
+
+namespace Unsupervised\Schedular\Payment;
+
+use Unsupervised\Schedular\Val;
+
+/**
+ * A studio credit held on a student's account — money already paid for a lesson
+ * that was later cancelled. Credits are consumed against future scheduled-billing
+ * charges (weekly / monthly) before the student is asked to pay, oldest first.
+ */
+class Credit {
+
+	public const STATUS_AVAILABLE = 'available';
+	public const STATUS_CONSUMED  = 'consumed';
+
+	/**
+	 * All valid credit statuses.
+	 *
+	 * @var list<string>
+	 */
+	public const VALID_STATUSES = [ self::STATUS_AVAILABLE, self::STATUS_CONSUMED ];
+
+	public function __construct(
+		public readonly int $studentId,
+		public readonly float $amount,
+		public readonly float $remaining,
+		public readonly string $currency = 'CAD',
+		public readonly ?int $sourcePaymentId = null,
+		public readonly ?int $sourceLessonId = null,
+		public readonly ?string $reason = null,
+		public readonly string $status = self::STATUS_AVAILABLE,
+		public readonly ?string $createdAt = null,
+		public readonly ?string $updatedAt = null,
+		public readonly ?int $id = null,
+	) {}
+
+	public static function fromRow( \stdClass $row ): self {
+		return new self(
+			studentId:       Val::int( $row->student_id ),
+			amount:          Val::float( $row->amount ),
+			remaining:       Val::float( $row->remaining ),
+			currency:        Val::string( $row->currency ),
+			sourcePaymentId: Val::intOrNull( $row->source_payment_id ?? null ),
+			sourceLessonId:  Val::intOrNull( $row->source_lesson_id ?? null ),
+			reason:          Val::stringOrNull( $row->reason ?? null ),
+			status:          Val::string( $row->status ),
+			createdAt:       Val::stringOrNull( $row->created_at ?? null ),
+			updatedAt:       Val::stringOrNull( $row->updated_at ?? null ),
+			id:              Val::int( $row->id ),
+		);
+	}
+
+	public function isAvailable(): bool {
+		return self::STATUS_AVAILABLE === $this->status && $this->remaining > 0.0;
+	}
+
+	/**
+	 * Returns a plain array representation of the credit.
+	 *
+	 * @return array<string, mixed>
+	 */
+	public function toArray(): array {
+		return [
+			'id'                => $this->id,
+			'student_id'        => $this->studentId,
+			'amount'            => $this->amount,
+			'remaining'         => $this->remaining,
+			'currency'          => $this->currency,
+			'source_payment_id' => $this->sourcePaymentId,
+			'source_lesson_id'  => $this->sourceLessonId,
+			'reason'            => $this->reason,
+			'status'            => $this->status,
+			'created_at'        => $this->createdAt,
+			'updated_at'        => $this->updatedAt,
+		];
+	}
+}

src/Payment/CreditRepository.php

@@ -0,0 +1,149 @@
+<?php
+declare(strict_types=1);
+
+namespace Unsupervised\Schedular\Payment;
+
+class CreditRepository {
+
+	private string $table;
+
+	public function __construct( private \wpdb $db ) {
+		$this->table = $db->prefix . 'us_credits';
+	}
+
+	public function insert( Credit $credit ): int {
+		$this->db->insert(
+			$this->table,
+			[
+				'student_id'        => $credit->studentId,
+				'amount'            => $credit->amount,
+				'remaining'         => $credit->remaining,
+				'currency'          => $credit->currency,
+				'source_payment_id' => $credit->sourcePaymentId,
+				'source_lesson_id'  => $credit->sourceLessonId,
+				'reason'            => $credit->reason,
+				'status'            => $credit->status,
+				'created_at'        => current_time( 'mysql' ),
+			],
+			[ '%d', '%f', '%f', '%s', '%d', '%d', '%s', '%s', '%s' ]
+		);
+
+		return $this->db->insert_id;
+	}
+
+	public function findById( int $id ): ?Credit {
+		$row = $this->db->get_row(
+			$this->db->prepare( 'SELECT * FROM %i WHERE id = %d', $this->table, $id )
+		);
+
+		return $row ? Credit::fromRow( $row ) : null;
+	}
+
+	/**
+	 * Whether a credit has already been issued for a cancelled lesson, so cancelling
+	 * (or re-cancelling) the same lesson never grants a second credit.
+	 */
+	public function existsForLesson( int $lessonId ): bool {
+		$found = $this->db->get_var(
+			$this->db->prepare(
+				'SELECT id FROM %i WHERE source_lesson_id = %d LIMIT 1',
+				$this->table,
+				$lessonId
+			)
+		);
+
+		return null !== $found;
+	}
+
+	/**
+	 * A student's total unused credit balance (sum of the remaining amounts of every
+	 * still-available credit).
+	 */
+	public function availableBalance( int $studentId ): float {
+		$total = $this->db->get_var(
+			$this->db->prepare(
+				'SELECT COALESCE( SUM( remaining ), 0 ) FROM %i WHERE student_id = %d AND status = %s',
+				$this->table,
+				$studentId,
+				Credit::STATUS_AVAILABLE
+			)
+		);
+
+		return round( (float) $total, 2 );
+	}
+
+	/**
+	 * A student's still-available credits, oldest first — the FIFO order they are
+	 * consumed in.
+	 *
+	 * @return list<Credit>
+	 */
+	public function findAvailableByStudent( int $studentId ): array {
+		$rows = $this->db->get_results(
+			$this->db->prepare(
+				'SELECT * FROM %i WHERE student_id = %d AND status = %s AND remaining > 0 ORDER BY created_at ASC, id ASC',
+				$this->table,
+				$studentId,
+				Credit::STATUS_AVAILABLE
+			)
+		);
+
+		return array_map( Credit::fromRow( ... ), $rows ?? [] );
+	}
+
+	/**
+	 * Every credit for a student, newest first (admin history).
+	 *
+	 * @return list<Credit>
+	 */
+	public function findByStudent( int $studentId ): array {
+		$rows = $this->db->get_results(
+			$this->db->prepare(
+				'SELECT * FROM %i WHERE student_id = %d ORDER BY created_at DESC, id DESC',
+				$this->table,
+				$studentId
+			)
+		);
+
+		return array_map( Credit::fromRow( ... ), $rows ?? [] );
+	}
+
+	/**
+	 * Draw down a student's credit balance by $amount, consuming their available
+	 * credits oldest first and marking each fully-spent credit `consumed`. Stops once
+	 * the amount is exhausted; a balance shorter than $amount simply drains to zero.
+	 */
+	public function consume( int $studentId, float $amount ): void {
+		$remaining = round( $amount, 2 );
+		if ( $remaining <= 0.0 ) {
+			return;
+		}
+
+		foreach ( $this->findAvailableByStudent( $studentId ) as $credit ) {
+			if ( $remaining <= 0.0 ) {
+				break;
+			}
+			if ( null === $credit->id ) {
+				continue;
+			}
+
+			$take         = min( $credit->remaining, $remaining );
+			$newRemaining = round( $credit->remaining - $take, 2 );
+			$status       = $newRemaining <= 0.0 ? Credit::STATUS_CONSUMED : Credit::STATUS_AVAILABLE;
+
+			$this->db->update(
+				$this->table,
+				[
+					'remaining'  => $newRemaining,
+					'status'     => $status,
+					'updated_at' => current_time( 'mysql' ),
+				],
+				[ 'id' => $credit->id ],
+				[ '%f', '%s', '%s' ],
+				[ '%d' ]
+			);
+
+			$remaining = round( $remaining - $take, 2 );
+		}
+	}
+}

src/Payment/Payment.php

@@ -44,6 +44,7 @@ class Payment {
 		public readonly string $status = self::STATUS_PENDING,
 		public readonly float $taxRate = 0.0,
 		public readonly float $taxAmount = 0.0,
+		public readonly float $creditApplied = 0.0,
 		public readonly ?string $dueDate = null,
 		public readonly ?string $periodKey = null,
 		public readonly ?string $noticeBatch = null,
@@ -68,6 +69,7 @@ class Payment {
 			status:                Val::string( $row->status ),
 			taxRate:               Val::float( $row->tax_rate ),
 			taxAmount:             Val::float( $row->tax_amount ),
+			creditApplied:         Val::float( $row->credit_applied ?? 0 ),
 			dueDate:               Val::stringOrNull( $row->due_date ?? null ),
 			periodKey:             Val::stringOrNull( $row->period_key ?? null ),
 			noticeBatch:           Val::stringOrNull( $row->notice_batch ?? null ),
@@ -101,6 +103,14 @@ class Payment {
 		return round( $this->amount + $this->taxAmount, 2 );
 	}
 
+	/**
+	 * What the student still owes after any account credit applied to this payment.
+	 * The full `total()` less `creditApplied`, floored at zero.
+	 */
+	public function netDue(): float {
+		return round( max( 0.0, $this->total() - $this->creditApplied ), 2 );
+	}
+
 	/**
 	 * Minimal payment info embedded in registration-creation responses: enough
 	 * for the front end to decide whether (and how) to run the payment step.
@@ -132,6 +142,8 @@ class Payment {
 			'tax_rate'          => $this->taxRate,
 			'tax_amount'        => $this->taxAmount,
 			'total'             => $this->total(),
+			'credit_applied'    => $this->creditApplied,
+			'net_due'           => $this->netDue(),
 			'currency'          => $this->currency,
 			'method'            => $this->method,
 			'status'            => $this->status,

src/Payment/PaymentController.php

@@ -65,11 +65,13 @@ class PaymentController {
 
 			$student = get_userdata( $payment->studentId );
 
-			$groups[ $key ]['total_raw'] += $payment->total();
+			// Show what the student still owes — the amount less any account credit
+			// already applied to this payment.
+			$groups[ $key ]['total_raw'] += $payment->netDue();
 			$groups[ $key ]['rows'][]     = [
 				'id'              => (int) $payment->id,
 				'student'         => $student ? $student->display_name : (string) $payment->studentId,
-				'amount'          => number_format( $payment->amount, 2 ) . ' ' . $payment->currency,
+				'amount'          => number_format( $payment->netDue(), 2 ) . ' ' . $payment->currency,
 				'method'          => $payment->method,
 				'for'             => $payment->registrationType . ' #' . $payment->registrationId,
 				'etransfer_email' => (string) $payment->etransferEmail,

src/Payment/PaymentDueMailer.php

@@ -17,9 +17,10 @@ class PaymentDueMailer {
 	 * on a lump-sum e-transfer so the studio can reconcile it to these payments.
 	 *
 	 * @param list<array{label: string, amount: float, currency: string, due_date: ?string, etransfer_email: ?string}> $items
+	 * @param float                                                                                                    $creditApplied Account credit deducted from the total this notice covers.
 	 * @return bool False when there is no recipient or nothing to bill.
 	 */
-	public function send( \WP_User $student, array $items, string $reference = '' ): bool {
+	public function send( \WP_User $student, array $items, string $reference = '', float $creditApplied = 0.0 ): bool {
 		if ( '' === (string) $student->user_email || [] === $items ) {
 			return false;
 		}
@@ -48,16 +49,30 @@ class PaymentDueMailer {
 			}
 		}
 
-		$body = __( 'You have upcoming payments due:', 'unsupervised-schedular' ) . "\n\n"
-			. implode( "\n", $lines ) . "\n\n"
-			. sprintf(
-				/* translators: 1: currency, 2: total amount */
-				__( 'Total due: %1$s %2$s', 'unsupervised-schedular' ),
-				$currency,
-				number_format( $total, 2 )
-			);
+		// Account credit (from an earlier cancelled paid lesson) offsets the total.
+		$creditApplied = round( min( $creditApplied, $total ), 2 );
+		$dueTotal      = round( $total - $creditApplied, 2 );
 
-		if ( [] !== $emails ) {
+		$body = __( 'You have upcoming payments due:', 'unsupervised-schedular' ) . "\n\n"
+			. implode( "\n", $lines );
+
+		if ( $creditApplied > 0.0 ) {
+			$body .= "\n\n" . sprintf(
+				/* translators: 1: currency, 2: credit amount */
+				__( 'Account credit applied: -%1$s %2$s', 'unsupervised-schedular' ),
+				$currency,
+				number_format( $creditApplied, 2 )
+			);
+		}
+
+		$body .= "\n\n" . sprintf(
+			/* translators: 1: currency, 2: total amount */
+			__( 'Total due: %1$s %2$s', 'unsupervised-schedular' ),
+			$currency,
+			number_format( $dueTotal, 2 )
+		);
+
+		if ( $dueTotal > 0.0 && [] !== $emails ) {
 			$body .= "\n\n" . sprintf(
 				/* translators: %s: e-transfer destination email address(es) */
 				__( 'Please send your e-transfer to: %s', 'unsupervised-schedular' ),

src/Payment/PaymentRepository.php

@@ -25,6 +25,7 @@ class PaymentRepository {
 				'status'                   => $payment->status,
 				'tax_rate'                 => $payment->taxRate,
 				'tax_amount'               => $payment->taxAmount,
+				'credit_applied'           => $payment->creditApplied,
 				'due_date'                 => $payment->dueDate,
 				'period_key'               => $payment->periodKey,
 				'notice_batch'             => $payment->noticeBatch,
@@ -35,7 +36,7 @@ class PaymentRepository {
 				'paid_at'                  => $payment->paidAt,
 				'created_at'               => current_time( 'mysql' ),
 			],
-			[ '%d', '%d', '%s', '%d', '%f', '%s', '%s', '%s', '%f', '%f', '%s', '%s', '%s', '%s', '%s', '%s', '%s', '%s', '%s' ]
+			[ '%d', '%d', '%s', '%d', '%f', '%s', '%s', '%s', '%f', '%f', '%f', '%s', '%s', '%s', '%s', '%s', '%s', '%s', '%s', '%s' ]
 		);
 
 		return $this->db->insert_id;
@@ -77,6 +78,22 @@ class PaymentRepository {
 		);
 	}
 
+	/**
+	 * Add to the account credit applied against a payment, reducing what the student
+	 * still owes on it (`Payment::netDue()`). Accumulates, so a second application
+	 * adds to the first.
+	 */
+	public function addCreditApplied( int $id, float $amount ): bool {
+		$sql = $this->db->prepare(
+			'UPDATE %i SET credit_applied = credit_applied + %f WHERE id = %d',
+			$this->table,
+			$amount,
+			$id
+		);
+
+		return null !== $sql && false !== $this->db->query( $sql );
+	}
+
 	/**
 	 * Set a payment's tax rate and recompute the tax amount from its subtotal.
 	 */

src/Payment/PaymentService.php

@@ -21,6 +21,7 @@ class PaymentService {
 		private EnrollmentRepository $enrollments,
 		private StudioSettings $settings,
 		private StripeGateway $stripe,
+		private CreditRepository $credits,
 	) {}
 
 	/**
@@ -134,6 +135,135 @@ class PaymentService {
 		}
 	}
 
+	/**
+	 * Credit a student for a cancelled lesson they had already paid for. The credit
+	 * is one lesson's share of the covering payment's total (including tax) — the
+	 * whole total for a single-lesson payment, or `total ÷ lessons covered` for a
+	 * payment that spans several (a monthly scheduled charge, or a weekly series paid
+	 * upfront). The original payment is left untouched; the credit is applied to the
+	 * student's future scheduled-billing charges. Returns null when the lesson was
+	 * never paid, has no covering payment, or was already credited.
+	 */
+	public function creditForCancelledLesson( Lesson $lesson ): ?Credit {
+		if ( null === $lesson->id ) {
+			return null;
+		}
+
+		$paymentId = $lesson->paymentId;
+		if ( null === $paymentId && null !== $lesson->seriesId ) {
+			// Series lessons other than the anchor carry no payment_id of their own;
+			// the whole reservation is paid through the anchor's payment.
+			$anchor    = $this->payments->findByRegistration( Payment::REG_LESSON, $lesson->seriesId );
+			$paymentId = $anchor?->id;
+		}
+		if ( null === $paymentId ) {
+			return null;
+		}
+
+		$payment = $this->payments->findById( $paymentId );
+		if ( null === $payment || ! $payment->isPaid() ) {
+			return null;
+		}
+
+		if ( $this->credits->existsForLesson( $lesson->id ) ) {
+			return null;
+		}
+
+		$share = round( $payment->total() / $this->coveredLessonCount( $lesson, $payment ), 2 );
+		if ( $share <= 0.0 ) {
+			return null;
+		}
+
+		$id = $this->credits->insert(
+			new Credit(
+				studentId:       $payment->studentId,
+				amount:          $share,
+				remaining:       $share,
+				currency:        $payment->currency,
+				sourcePaymentId: $payment->id,
+				sourceLessonId:  $lesson->id,
+				reason:          sprintf(
+					/* translators: %d: cancelled lesson id */
+					__( 'Credit for cancelled lesson #%d', 'unsupervised-schedular' ),
+					$lesson->id
+				),
+			)
+		);
+
+		return $this->credits->findById( $id );
+	}
+
+	/**
+	 * How many lessons the covering payment was billed for, so its total can be split
+	 * into a per-lesson credit. A weekly series paid upfront (unscheduled) covers the
+	 * whole series; every other case — a single booking, a weekly scheduled lesson
+	 * (one payment each), or a monthly scheduled charge (payment linked to each
+	 * lesson) — is answered by how many lessons point at the payment. Never below one.
+	 */
+	private function coveredLessonCount( Lesson $lesson, Payment $payment ): int {
+		if ( ! $payment->isScheduled() && null !== $lesson->seriesId ) {
+			return max( 1, $this->bookings->countBySeries( $lesson->seriesId ) );
+		}
+
+		return max( 1, $this->bookings->countByPaymentId( (int) $payment->id ) );
+	}
+
+	/**
+	 * Apply a student's available credit balance against a set of freshly-created
+	 * pending payments (the ones a billing scan just generated for them), oldest
+	 * charge first. Each payment's `credit_applied` is raised by the amount covered;
+	 * a payment fully covered is marked paid-by-credit and its registration confirmed
+	 * so it leaves the confirmation queue. The credit ledger is drawn down by the
+	 * total applied. Returns a map of payment id to the credit applied to it, so the
+	 * caller can reflect the reduction on the student's notice.
+	 *
+	 * @param list<Payment> $payments
+	 * @return array<int, float>
+	 */
+	public function applyCredits( int $studentId, array $payments ): array {
+		$balance = $this->credits->availableBalance( $studentId );
+		if ( $balance <= 0.0 ) {
+			return [];
+		}
+
+		$applied  = [];
+		$consumed = 0.0;
+
+		foreach ( $payments as $payment ) {
+			if ( null === $payment->id || $balance <= 0.0 ) {
+				continue;
+			}
+
+			$owing = $payment->netDue();
+			if ( $owing <= 0.0 ) {
+				continue;
+			}
+
+			$amount = round( min( $balance, $owing ), 2 );
+			if ( $amount <= 0.0 ) {
+				continue;
+			}
+
+			$this->payments->addCreditApplied( $payment->id, $amount );
+
+			// Fully covered by credit: settle it so it drops out of the pending queue.
+			if ( $amount >= $owing ) {
+				$this->payments->markPaid( $payment->id, 'USC-' . $payment->id );
+				$this->confirmRegistration( $payment->registrationType, $payment->registrationId );
+			}
+
+			$applied[ $payment->id ] = $amount;
+			$balance                 = round( $balance - $amount, 2 );
+			$consumed                = round( $consumed + $amount, 2 );
+		}
+
+		if ( $consumed > 0.0 ) {
+			$this->credits->consume( $studentId, $consumed );
+		}
+
+		return $applied;
+	}
+
 	/**
 	 * Resolve the client-side payment step for a freshly created registration.
 	 * For a card payment a Stripe PaymentIntent is created (or replayed

src/Payment/ScheduledBillingRunner.php

@@ -44,16 +44,16 @@ class ScheduledBillingRunner {
 
 		// One notice bucket per student, filled as pending payments are created and
 		// flushed to a single email at the end, so a student billed for several
-		// lessons on one day is emailed once — never once per lesson. $batchIds
-		// tracks the payment ids behind each student's bucket so they can be tagged
-		// with a shared reference for lump-sum e-transfer reconciliation.
-		$buckets  = [];
-		$batchIds = [];
+		// lessons on one day is emailed once — never once per lesson. Each entry keeps
+		// the created payment and its label; credits are applied across the whole
+		// bucket before the notice is built, so a student's account credit offsets the
+		// run's charges oldest-first.
+		$buckets = [];
 
-		$this->billPrivateLessons( $now, $buckets, $batchIds );
-		$this->billGroupEnrollments( $now, $buckets, $batchIds );
+		$this->billPrivateLessons( $now, $buckets );
+		$this->billGroupEnrollments( $now, $buckets );
 
-		$this->sendNotices( $buckets, $batchIds );
+		$this->sendNotices( $buckets );
 	}
 
 	/**
@@ -61,10 +61,9 @@ class ScheduledBillingRunner {
 	 * are within 24 hours; monthly lessons are grouped per calendar month and billed
 	 * one payment for the month once its 1st has arrived.
 	 *
-	 * @param array<int, list<array{label: string, amount: float, currency: string, due_date: ?string, etransfer_email: ?string}>> $buckets
-	 * @param array<int, list<int>> $batchIds
+	 * @param array<int, list<array{payment: Payment, label: string}>> $buckets
 	 */
-	private function billPrivateLessons( \DateTimeImmutable $now, array &$buckets, array &$batchIds ): void {
+	private function billPrivateLessons( \DateTimeImmutable $now, array &$buckets ): void {
 		$today   = $now->format( 'Y-m-d' );
 		$monthly = [];
 
@@ -109,7 +108,6 @@ class ScheduledBillingRunner {
 
 			$this->bill(
 				$buckets,
-				$batchIds,
 				Payment::REG_LESSON,
 				$lessonId,
 				$studentId,
@@ -123,7 +121,7 @@ class ScheduledBillingRunner {
 			);
 		}
 
-		$this->billMonthlyLessonGroups( $today, $monthly, $buckets, $batchIds );
+		$this->billMonthlyLessonGroups( $today, $monthly, $buckets );
 	}
 
 	/**
@@ -132,10 +130,9 @@ class ScheduledBillingRunner {
 	 * lesson in the group; the rest are pointed at it so they are not re-billed.
 	 *
 	 * @param array<string, list<array{lesson_id: int, student_id: int, instructor_id: int, currency: string, etransfer: ?string, title: string, price: float, start: \DateTimeImmutable}>> $monthly
-	 * @param array<int, list<array{label: string, amount: float, currency: string, due_date: ?string, etransfer_email: ?string}>> $buckets
-	 * @param array<int, list<int>> $batchIds
+	 * @param array<int, list<array{payment: Payment, label: string}>> $buckets
 	 */
-	private function billMonthlyLessonGroups( string $today, array $monthly, array &$buckets, array &$batchIds ): void {
+	private function billMonthlyLessonGroups( string $today, array $monthly, array &$buckets ): void {
 		foreach ( $monthly as $group ) {
 			$first      = $group[0]['start'];
 			$monthStart = $first->format( 'Y-m-01' );
@@ -151,7 +148,6 @@ class ScheduledBillingRunner {
 
 			$payment = $this->bill(
 				$buckets,
-				$batchIds,
 				Payment::REG_LESSON,
 				$anchorId,
 				$group[0]['student_id'],
@@ -188,10 +184,9 @@ class ScheduledBillingRunner {
 	 * per month (on the 1st) for that month's sessions. Dedup is by `period_key`
 	 * since a single enrolment maps to many periodic charges.
 	 *
-	 * @param array<int, list<array{label: string, amount: float, currency: string, due_date: ?string, etransfer_email: ?string}>> $buckets
-	 * @param array<int, list<int>> $batchIds
+	 * @param array<int, list<array{payment: Payment, label: string}>> $buckets
 	 */
-	private function billGroupEnrollments( \DateTimeImmutable $now, array &$buckets, array &$batchIds ): void {
+	private function billGroupEnrollments( \DateTimeImmutable $now, array &$buckets ): void {
 		$today     = $now->format( 'Y-m-d' );
 		$offerings = [];
 
@@ -211,9 +206,9 @@ class ScheduledBillingRunner {
 			}
 
 			if ( Offering::BILLING_MONTHLY === $offering->billingMode ) {
-				$this->billGroupMonthly( $now, $today, $enrollment, $offering, $windows, $buckets, $batchIds );
+				$this->billGroupMonthly( $now, $today, $enrollment, $offering, $windows, $buckets );
 			} else {
-				$this->billGroupWeekly( $now, $enrollment, $offering, $windows, $buckets, $batchIds );
+				$this->billGroupWeekly( $now, $enrollment, $offering, $windows, $buckets );
 			}
 		}
 	}
@@ -222,10 +217,9 @@ class ScheduledBillingRunner {
 	 * Bill one payment per group-class session that is now within 24 hours.
 	 *
 	 * @param list<array{start: string, end: string}> $windows
-	 * @param array<int, list<array{label: string, amount: float, currency: string, due_date: ?string, etransfer_email: ?string}>> $buckets
-	 * @param array<int, list<int>> $batchIds
+	 * @param array<int, list<array{payment: Payment, label: string}>> $buckets
 	 */
-	private function billGroupWeekly( \DateTimeImmutable $now, Enrollment $enrollment, Offering $offering, array $windows, array &$buckets, array &$batchIds ): void {
+	private function billGroupWeekly( \DateTimeImmutable $now, Enrollment $enrollment, Offering $offering, array $windows, array &$buckets ): void {
 		foreach ( $windows as $window ) {
 			$start = new \DateTimeImmutable( $window['start'] );
 			$due   = $start->modify( '-1 day' );
@@ -240,7 +234,6 @@ class ScheduledBillingRunner {
 
 			$this->bill(
 				$buckets,
-				$batchIds,
 				Payment::REG_ENROLLMENT,
 				(int) $enrollment->id,
 				$enrollment->studentId,
@@ -259,10 +252,9 @@ class ScheduledBillingRunner {
 	 * Bill one payment per calendar month of a group class, once its 1st arrives.
 	 *
 	 * @param list<array{start: string, end: string}> $windows
-	 * @param array<int, list<array{label: string, amount: float, currency: string, due_date: ?string, etransfer_email: ?string}>> $buckets
-	 * @param array<int, list<int>> $batchIds
+	 * @param array<int, list<array{payment: Payment, label: string}>> $buckets
 	 */
-	private function billGroupMonthly( \DateTimeImmutable $now, string $today, Enrollment $enrollment, Offering $offering, array $windows, array &$buckets, array &$batchIds ): void { // phpcs:ignore Generic.CodeAnalysis.UnusedFunctionParameter.Found
+	private function billGroupMonthly( \DateTimeImmutable $now, string $today, Enrollment $enrollment, Offering $offering, array $windows, array &$buckets ): void { // phpcs:ignore Generic.CodeAnalysis.UnusedFunctionParameter.Found
 		// Count this enrolment's sessions per calendar month.
 		$months = [];
 		foreach ( $windows as $window ) {
@@ -282,7 +274,6 @@ class ScheduledBillingRunner {
 
 			$this->bill(
 				$buckets,
-				$batchIds,
 				Payment::REG_ENROLLMENT,
 				(int) $enrollment->id,
 				$enrollment->studentId,
@@ -305,46 +296,72 @@ class ScheduledBillingRunner {
 
 	/**
 	 * Create one scheduled payment and, when it is pending (not a comp auto-pay),
-	 * add an itemised line to the student's notice bucket and record its payment id
-	 * for the shared notice batch. Returns the created payment, or null when there
-	 * was nothing to charge.
+	 * add it to the student's notice bucket with the label to show on the notice.
+	 * Credits are applied later, once the whole bucket is known. Returns the created
+	 * payment, or null when there was nothing to charge.
 	 *
-	 * @param array<int, list<array{label: string, amount: float, currency: string, due_date: ?string, etransfer_email: ?string}>> $buckets
-	 * @param array<int, list<int>> $batchIds
+	 * @param array<int, list<array{payment: Payment, label: string}>> $buckets
 	 */
-	private function bill( array &$buckets, array &$batchIds, string $type, int $registrationId, int $studentId, int $instructorId, float $amount, string $currency, ?string $etransferEmail, string $dueDate, string $periodKey, string $label ): ?Payment {
+	private function bill( array &$buckets, string $type, int $registrationId, int $studentId, int $instructorId, float $amount, string $currency, ?string $etransferEmail, string $dueDate, string $periodKey, string $label ): ?Payment {
 		$payment = $this->payments->createForRegistration( $type, $registrationId, $studentId, $instructorId, $amount, $currency, $etransferEmail, $dueDate, $periodKey );
 
 		if ( null !== $payment && null !== $payment->id && Payment::STATUS_PENDING === $payment->status ) {
-			$buckets[ $studentId ][]  = [
-				'label'           => $label,
-				'amount'          => $payment->total(),
-				'currency'        => $payment->currency,
-				'due_date'        => $payment->dueDate,
-				'etransfer_email' => $payment->etransferEmail,
+			$buckets[ $studentId ][] = [
+				'payment' => $payment,
+				'label'   => $label,
 			];
-			$batchIds[ $studentId ][] = $payment->id;
 		}
 
 		return $payment;
 	}
 
 	/**
-	 * Tag each student's payments with a shared batch reference and email them one
-	 * itemised notice quoting it, so a lump-sum e-transfer can be reconciled to the
-	 * exact pending payments it covers.
+	 * For each student, apply any account credit they hold against the run's charges,
+	 * tag the payments they still owe with a shared batch reference, and email them
+	 * one itemised notice. The notice lists each charge at its full amount, then the
+	 * credit applied and the reduced total due; a charge fully covered by credit is
+	 * already settled and carries no reference. A lump-sum e-transfer for the balance
+	 * reconciles to the reference.
 	 *
-	 * @param array<int, list<array{label: string, amount: float, currency: string, due_date: ?string, etransfer_email: ?string}>> $buckets
-	 * @param array<int, list<int>> $batchIds
+	 * @param array<int, list<array{payment: Payment, label: string}>> $buckets
 	 */
-	private function sendNotices( array $buckets, array $batchIds ): void {
-		foreach ( $buckets as $studentId => $items ) {
-			$reference = $this->reference();
-			$this->payments->assignNoticeBatch( $batchIds[ $studentId ] ?? [], $reference );
+	private function sendNotices( array $buckets ): void {
+		foreach ( $buckets as $studentId => $entries ) {
+			$payments = array_map( static fn( array $entry ): Payment => $entry['payment'], $entries );
+			$applied  = $this->payments->applyCredits( $studentId, $payments );
+
+			$items       = [];
+			$batchIds    = [];
+			$creditTotal = 0.0;
+
+			foreach ( $entries as $entry ) {
+				$payment  = $entry['payment'];
+				$id       = (int) $payment->id;
+				$credited = $applied[ $id ] ?? 0.0;
+
+				$creditTotal += $credited;
+
+				$items[] = [
+					'label'           => $entry['label'],
+					'amount'          => $payment->total(),
+					'currency'        => $payment->currency,
+					'due_date'        => $payment->dueDate,
+					'etransfer_email' => $payment->etransferEmail,
+				];
+
+				// A charge still carrying a balance is what a lump-sum e-transfer covers;
+				// one fully settled by credit needs no reconciliation reference.
+				if ( round( $payment->total() - $credited, 2 ) > 0.0 ) {
+					$batchIds[] = $id;
+				}
+			}
+
+			$reference = [] !== $batchIds ? $this->reference() : '';
+			$this->payments->assignNoticeBatch( $batchIds, $reference );
 
 			$user = get_userdata( $studentId );
 			if ( $user instanceof \WP_User ) {
-				$this->mailer->send( $user, $items, $reference );
+				$this->mailer->send( $user, $items, $reference, round( $creditTotal, 2 ) );
 			}
 		}
 	}

src/Plugin.php

@@ -18,6 +18,7 @@ use Unsupervised\Schedular\GroupClass\GroupAccessRepository;
 use Unsupervised\Schedular\GroupClass\GroupClassPage;
 use Unsupervised\Schedular\Offering\OfferingRepository;
 use Unsupervised\Schedular\Payment\BillingMethodResolver;
+use Unsupervised\Schedular\Payment\CreditRepository;
 use Unsupervised\Schedular\Payment\PaymentRepository;
 use Unsupervised\Schedular\Payment\PaymentDueMailer;
 use Unsupervised\Schedular\Payment\PaymentService;
@@ -65,10 +66,11 @@ class Plugin {
 		$registrationGate = new RegistrationGate( $questions, $answers, $policies, $policyVersions, $acceptances );
 
 		$paymentRepo    = new PaymentRepository( $wpdb );
+		$creditRepo     = new CreditRepository( $wpdb );
 		$settings       = new StudioSettings();
 		$resolver       = new BillingMethodResolver( $settings );
 		$stripe         = new StripeGateway( $settings );
-		$paymentService = new PaymentService( $paymentRepo, $resolver, new ReceiptMailer(), $bookings, $enrollments, $settings, $stripe );
+		$paymentService = new PaymentService( $paymentRepo, $resolver, new ReceiptMailer(), $bookings, $enrollments, $settings, $stripe, $creditRepo );
 
 		// The shortcode and block wrappers share the same page objects so
 		// front-end output is identical whichever way a page embeds them.
@@ -85,7 +87,7 @@ class Plugin {
 		( new RoleManager() )->register();
 		( new RegistrationLoginGate() )->register();
 		( new EmailConfirmationHandler( $settings, $registrationMailer ) )->register();
-		( new AdminMenu( $availability, $bookings, $offerings, $questions, $answers, $policies, $policyVersions, $policyService, $acceptances, $invites, $enrollments, $groupAccess, $settings, $paymentRepo, $paymentService, $resolver, $registrationMailer ) )->register();
+		( new AdminMenu( $availability, $bookings, $offerings, $questions, $answers, $policies, $policyVersions, $policyService, $acceptances, $invites, $enrollments, $groupAccess, $settings, $paymentRepo, $paymentService, $resolver, $registrationMailer, $creditRepo ) )->register();
 		( new RestRegistrar( $availability, $bookings, $offerings, $questions, $policies, $policyVersions, $policyService, $registrationGate, $enrollments, $groupAccess, $paymentService ) )->register();
 		( new ShortcodeRegistrar( $bookingPage, $loginPage, $registrationPage, $groupClassPage ) )->register();
 		( new BlockRegistrar( $bookingPage, $loginPage, $registrationPage, $groupClassPage ) )->register();

src/Schema.php

@@ -159,6 +159,7 @@ class Schema {
                 status                   VARCHAR(20)     NOT NULL DEFAULT 'pending',
                 tax_rate                 DECIMAL(5,2)    NOT NULL DEFAULT 0,
                 tax_amount               DECIMAL(10,2)   NOT NULL DEFAULT 0,
+                credit_applied           DECIMAL(10,2)   NOT NULL DEFAULT 0,
                 due_date                 DATE            DEFAULT NULL,
                 period_key               VARCHAR(20)     DEFAULT NULL,
                 notice_batch             VARCHAR(32)     DEFAULT NULL,
@@ -175,6 +176,24 @@ class Schema {
                 KEY status (status)
             ) {$charset};",
 
+			"CREATE TABLE {$prefix}us_credits (
+                id                BIGINT UNSIGNED NOT NULL AUTO_INCREMENT,
+                student_id        BIGINT UNSIGNED NOT NULL,
+                amount            DECIMAL(10,2)   NOT NULL DEFAULT 0,
+                remaining         DECIMAL(10,2)   NOT NULL DEFAULT 0,
+                currency          VARCHAR(3)      NOT NULL DEFAULT 'CAD',
+                source_payment_id BIGINT UNSIGNED DEFAULT NULL,
+                source_lesson_id  BIGINT UNSIGNED DEFAULT NULL,
+                reason            VARCHAR(191)    DEFAULT NULL,
+                status            VARCHAR(20)     NOT NULL DEFAULT 'available',
+                created_at        DATETIME        NOT NULL,
+                updated_at        DATETIME        DEFAULT NULL,
+                PRIMARY KEY (id),
+                KEY student_id (student_id),
+                KEY status (status),
+                KEY source_lesson_id (source_lesson_id)
+            ) {$charset};",
+
 			"CREATE TABLE {$prefix}us_group_enrollments (
                 id            BIGINT UNSIGNED NOT NULL AUTO_INCREMENT,
                 offering_id   BIGINT UNSIGNED NOT NULL,