CHANGELOG.md

@@ -11,6 +11,11 @@ When a `v*` tag is pushed, `.gitea/workflows/release.yml` publishes the matching
 the plugin to the next patch version and adds a fresh section here for it. Record
 each change under the current top section as you work.
 
+## [1.6.0]
+
+### Added
+- **You can now read, rewrite and preview the "Payment due" email, on Studio Settings → Payment Due Email.** The notice a family gets when the daily scan finds lessons to pay for was fixed wording baked into the plugin; now its subject and body sit in an editor you can change to match how your studio talks to its students. Drop in `{student_name}`, `{items}`, `{total_due}` and the rest wherever you want them, and a preview below fills those tokens with sample values and updates as you type, so you see the actual email a scan would send before you save. Leave a field blank to fall back to the built-in wording, or use the reset button to restore all of it at once. Nothing about how or when the email is sent changes — only what it says — and until you touch it, students receive exactly the notice they always did.
+
 ## [1.5.8]
 
 ### Added

assets/js/payment-email-admin.js

@@ -0,0 +1,60 @@
+/**
+ * Payment due email editor: live preview.
+ *
+ * Posts the subject/body/item-line the admin is editing to the read-only preview
+ * REST endpoint and swaps the rendered result into the preview panel, debounced
+ * as they type. The server always renders from the same sample values, so this
+ * mirrors exactly what a real billing scan would send. Purely a convenience — the
+ * page already shows a server-rendered preview of the saved template without it.
+ */
+(function () {
+    'use strict';
+
+    const config = window.uscPaymentEmailPreview;
+    if (!config || !config.url) return;
+
+    const subjectEl  = document.getElementById('usc-pe-subject');
+    const bodyEl      = document.getElementById('usc-pe-body');
+    const itemLineEl  = document.getElementById('usc-pe-item-line');
+    const outSubject  = document.getElementById('usc-pe-preview-subject');
+    const outBody     = document.getElementById('usc-pe-preview-body');
+
+    if (!subjectEl || !bodyEl || !itemLineEl || !outSubject || !outBody) return;
+
+    let timer = null;
+
+    function refresh() {
+        fetch(config.url, {
+            method: 'POST',
+            headers: {
+                'Content-Type': 'application/json',
+                'X-WP-Nonce': config.nonce
+            },
+            body: JSON.stringify({
+                subject: subjectEl.value,
+                body: bodyEl.value,
+                item_line: itemLineEl.value
+            })
+        })
+            .then(function (response) {
+                if (!response.ok) throw new Error('preview failed');
+                return response.json();
+            })
+            .then(function (data) {
+                outSubject.textContent = data.subject || '';
+                outBody.textContent = data.body || '';
+            })
+            .catch(function () {
+                // Leave the last good preview in place on error.
+            });
+    }
+
+    function schedule() {
+        if (timer) window.clearTimeout(timer);
+        timer = window.setTimeout(refresh, 300);
+    }
+
+    [subjectEl, bodyEl, itemLineEl].forEach(function (el) {
+        el.addEventListener('input', schedule);
+    });
+})();

src/AdminMenu.php

@@ -32,6 +32,7 @@ use Unsupervised\Schedular\Offering\OfferingRepository;
 use Unsupervised\Schedular\Payment\BillingMethodResolver;
 use Unsupervised\Schedular\Payment\CreditRepository;
 use Unsupervised\Schedular\Payment\PaymentController;
+use Unsupervised\Schedular\Payment\PaymentEmailController;
 use Unsupervised\Schedular\Payment\PaymentReportController;
 use Unsupervised\Schedular\Payment\PaymentRepository;
 use Unsupervised\Schedular\Payment\PaymentService;
@@ -56,6 +57,12 @@ class AdminMenu {
 	 */
 	private string $availabilityHook = '';
 
+	/**
+	 * Hook suffix of the payment-email screen, captured when the page is added so
+	 * its live-preview script loads on that screen only.
+	 */
+	private string $paymentEmailHook = '';
+
 	private AvailabilityController $availabilityController;
 	private LessonController $lessonController;
 	private OfferingController $offeringController;
@@ -69,6 +76,7 @@ class AdminMenu {
 	private StudioSettings $settings;
 	private AccessSettings $accessSettings;
 	private PaymentController $paymentController;
+	private PaymentEmailController $paymentEmailController;
 	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, CreditRepository $credits, GuardianService $guardians, LessonBooker $booker, RegistrationGate $gate, BillingModeReconciler $billingModeReconciler ) {
@@ -90,6 +98,7 @@ class AdminMenu {
 		$this->settings                       = $settings;
 		$this->accessSettings                 = new AccessSettings();
 		$this->paymentController              = new PaymentController( $payments, $paymentService );
+		$this->paymentEmailController         = new PaymentEmailController();
 		$this->paymentReportController        = new PaymentReportController( $payments );
 	}
 
@@ -105,17 +114,26 @@ class AdminMenu {
 	 * @param string $hookSuffix Screen the enqueue is running for.
 	 */
 	public function enqueueAssets( string $hookSuffix ): void {
-		if ( '' === $this->availabilityHook || $hookSuffix !== $this->availabilityHook ) {
+		if ( '' !== $this->availabilityHook && $hookSuffix === $this->availabilityHook ) {
+			wp_enqueue_script(
+				'us-scheduler-availability-admin',
+				USC_PLUGIN_URL . 'assets/js/availability-admin.js',
+				[],
+				USC_VERSION,
+				true
+			);
 			return;
 		}
 
-		wp_enqueue_script(
-			'us-scheduler-availability-admin',
-			USC_PLUGIN_URL . 'assets/js/availability-admin.js',
-			[],
-			USC_VERSION,
-			true
-		);
+		if ( '' !== $this->paymentEmailHook && $hookSuffix === $this->paymentEmailHook ) {
+			wp_enqueue_script(
+				'us-scheduler-payment-email-admin',
+				USC_PLUGIN_URL . 'assets/js/payment-email-admin.js',
+				[],
+				USC_VERSION,
+				true
+			);
+		}
 	}
 
 	public function addPages(): void {
@@ -263,6 +281,16 @@ class AdminMenu {
 			30
 		);
 
+		// Studio admin: view, edit and preview the payment-due email template.
+		$this->paymentEmailHook = (string) add_submenu_page(
+			'us-settings',
+			__( 'Payment Due Email', 'unsupervised-schedular' ),
+			__( 'Payment Due Email', 'unsupervised-schedular' ),
+			RoleManager::CAP_MANAGE_BILLING,
+			'us-payment-email',
+			[ $this->paymentEmailController, 'renderPage' ]
+		);
+
 		// Site owner: whether WordPress administrators are studio admins / instructors.
 		// Gated on the core manage_options capability — never the plugin's own grants —
 		// so an administrator can always reach it to re-enable a disabled grant.

src/Payment/PaymentDueEmailTemplate.php

@@ -0,0 +1,130 @@
+<?php
+declare(strict_types=1);
+
+namespace Unsupervised\Schedular\Payment;
+
+use Unsupervised\Schedular\Val;
+
+/**
+ * The editable payment-due email: its subject and body are stored as WordPress
+ * options (falling back to built-in defaults) and rendered by substituting a
+ * small set of `{token}` placeholders with the values the daily billing scan
+ * gathered for a student.
+ *
+ * The body carries an {items} block — one line per charge — and optional
+ * {credit}, {etransfer} and {reference} blocks that the renderer collapses to
+ * nothing when they do not apply, so a studio admin never has to hand-edit
+ * conditional prose.
+ */
+class PaymentDueEmailTemplate {
+
+	public const OPT_SUBJECT   = 'us_payment_due_email_subject';
+	public const OPT_BODY      = 'us_payment_due_email_body';
+	public const OPT_ITEM_LINE = 'us_payment_due_email_item_line';
+
+	/**
+	 * Tokens the admin may drop into the subject/body, mapped to a short
+	 * translated description shown beside the editor. `{items}` expands to the
+	 * itemised list rendered from the item-line template; the credit/etransfer/
+	 * reference tokens are whole lines that vanish when not applicable.
+	 *
+	 * @return array<string, string>
+	 */
+	public static function tokens(): array {
+		return [
+			'{student_name}' => __( "The student's display name.", 'unsupervised-schedular' ),
+			'{items}'        => __( 'The itemised list of charges (one line each).', 'unsupervised-schedular' ),
+			'{total_due}'    => __( 'The grand total due, e.g. CAD 75.00.', 'unsupervised-schedular' ),
+			'{credit}'       => __( 'Account-credit line; empty when no credit applies.', 'unsupervised-schedular' ),
+			'{etransfer}'    => __( 'E-transfer destination line; empty when nothing is owed.', 'unsupervised-schedular' ),
+			'{reference}'    => __( 'Payment reference line; empty when no reference is set.', 'unsupervised-schedular' ),
+		];
+	}
+
+	/**
+	 * Tokens the item-line template understands, one charge at a time.
+	 *
+	 * @return array<string, string>
+	 */
+	public static function itemTokens(): array {
+		return [
+			'{label}'    => __( 'The charge description, e.g. Piano.', 'unsupervised-schedular' ),
+			'{due_date}' => __( 'The due date, e.g. Jul 15, 2026.', 'unsupervised-schedular' ),
+			'{currency}' => __( 'The currency code, e.g. CAD.', 'unsupervised-schedular' ),
+			'{amount}'   => __( 'The charge amount, e.g. 35.00.', 'unsupervised-schedular' ),
+		];
+	}
+
+	public static function defaultSubject(): string {
+		return __( 'Payment due', 'unsupervised-schedular' );
+	}
+
+	public static function defaultBody(): string {
+		return __(
+			"You have upcoming payments due:\n\n{items}{credit}\n\nTotal due: {total_due}{etransfer}{reference}",
+			'unsupervised-schedular'
+		);
+	}
+
+	public static function defaultItemLine(): string {
+		/* translators: this is a template with tokens; keep the {tokens} intact. */
+		return __( '- {label} (due {due_date}): {currency} {amount}', 'unsupervised-schedular' );
+	}
+
+	public function subject(): string {
+		$stored = Val::string( get_option( self::OPT_SUBJECT, '' ) );
+
+		return '' !== $stored ? $stored : self::defaultSubject();
+	}
+
+	public function body(): string {
+		$stored = Val::string( get_option( self::OPT_BODY, '' ) );
+
+		return '' !== $stored ? $stored : self::defaultBody();
+	}
+
+	public function itemLine(): string {
+		$stored = Val::string( get_option( self::OPT_ITEM_LINE, '' ) );
+
+		return '' !== $stored ? $stored : self::defaultItemLine();
+	}
+
+	public function saveSubject( string $subject ): void {
+		update_option( self::OPT_SUBJECT, $subject );
+	}
+
+	public function saveBody( string $body ): void {
+		update_option( self::OPT_BODY, $body );
+	}
+
+	public function saveItemLine( string $itemLine ): void {
+		update_option( self::OPT_ITEM_LINE, $itemLine );
+	}
+
+	/**
+	 * Render the stored subject template with the given token values.
+	 *
+	 * @param array<string, string> $tokens Token => replacement (keys include the braces).
+	 */
+	public function renderSubject( array $tokens ): string {
+		return strtr( $this->subject(), $tokens );
+	}
+
+	/**
+	 * Render the stored body template with the given token values.
+	 *
+	 * @param array<string, string> $tokens Token => replacement (keys include the braces).
+	 */
+	public function renderBody( array $tokens ): string {
+		return strtr( $this->body(), $tokens );
+	}
+
+	/**
+	 * Render one itemised charge line from the stored item-line template.
+	 *
+	 * @param array<string, string> $tokens Item token => replacement (keys include the braces).
+	 */
+	public function renderItemLine( array $tokens ): string {
+		return strtr( $this->itemLine(), $tokens );
+	}
+}

src/Payment/PaymentDueMailer.php

@@ -8,9 +8,16 @@ namespace Unsupervised\Schedular\Payment;
  * scan generated for them in one run, so a student billed for several lessons on
  * the same day receives one email with a line per item and a grand total — never
  * one email per lesson.
+ *
+ * The subject and body come from {@see PaymentDueEmailTemplate}, an
+ * admin-editable template of `{token}` placeholders; this class gathers the
+ * values for those tokens (items list, totals, credit/e-transfer/reference
+ * lines) and asks the template to render them.
  */
 class PaymentDueMailer {
 
+	public function __construct( private PaymentDueEmailTemplate $template = new PaymentDueEmailTemplate() ) {}
+
 	/**
 	 * Send one student their consolidated due-payment notice for the current scan.
 	 * The optional `$reference` is the shared notice-batch code the student can quote
@@ -25,6 +32,29 @@ class PaymentDueMailer {
 			return false;
 		}
 
+		$tokens = $this->buildTokens(
+			(string) $student->display_name,
+			$items,
+			$reference,
+			$creditApplied
+		);
+
+		return (bool) wp_mail(
+			$student->user_email,
+			$this->template->renderSubject( $tokens ),
+			$this->template->renderBody( $tokens )
+		);
+	}
+
+	/**
+	 * Build the full token map the subject/body templates are rendered against,
+	 * from the same data the daily scan hands the mailer. Exposed so the admin
+	 * preview can render the exact email a real scan would produce.
+	 *
+	 * @param list<array{label: string, amount: float, currency: string, due_date: ?string, etransfer_email: ?string}> $items
+	 * @return array<string, string>
+	 */
+	public function buildTokens( string $studentName, array $items, string $reference = '', float $creditApplied = 0.0 ): array {
 		$currency = (string) $items[0]['currency'];
 		$total    = 0.0;
 		$lines    = [];
@@ -34,13 +64,13 @@ class PaymentDueMailer {
 			$amount = (float) $item['amount'];
 			$total += $amount;
 
-			$lines[] = sprintf(
-				/* translators: 1: item description, 2: due date, 3: currency, 4: amount */
-				__( '- %1$s (due %2$s): %3$s %4$s', 'unsupervised-schedular' ),
-				(string) $item['label'],
-				$this->formatDate( $item['due_date'] ?? null ),
-				$currency,
-				number_format( $amount, 2 )
+			$lines[] = $this->template->renderItemLine(
+				[
+					'{label}'    => (string) $item['label'],
+					'{due_date}' => $this->formatDate( $item['due_date'] ?? null ),
+					'{currency}' => $currency,
+					'{amount}'   => number_format( $amount, 2 ),
+				]
 			);
 
 			$etransfer = (string) ( $item['etransfer_email'] ?? '' );
@@ -53,11 +83,9 @@ class PaymentDueMailer {
 		$creditApplied = round( min( $creditApplied, $total ), 2 );
 		$dueTotal      = round( $total - $creditApplied, 2 );
 
-		$body = __( 'You have upcoming payments due:', 'unsupervised-schedular' ) . "\n\n"
-			. implode( "\n", $lines );
-
+		$credit = '';
 		if ( $creditApplied > 0.0 ) {
-			$body .= "\n\n" . sprintf(
+			$credit = "\n\n" . sprintf(
 				/* translators: 1: currency, 2: credit amount */
 				__( 'Account credit applied: -%1$s %2$s', 'unsupervised-schedular' ),
 				$currency,
@@ -65,30 +93,32 @@ class PaymentDueMailer {
 			);
 		}
 
-		$body .= "\n\n" . sprintf(
-			/* translators: 1: currency, 2: total amount */
-			__( 'Total due: %1$s %2$s', 'unsupervised-schedular' ),
-			$currency,
-			number_format( $dueTotal, 2 )
-		);
-
+		$etransfer = '';
 		if ( $dueTotal > 0.0 && [] !== $emails ) {
-			$body .= "\n\n" . sprintf(
+			$etransfer = "\n\n" . sprintf(
 				/* translators: %s: e-transfer destination email address(es) */
 				__( 'Please send your e-transfer to: %s', 'unsupervised-schedular' ),
 				implode( ', ', array_keys( $emails ) )
 			);
 		}
 
+		$referenceLine = '';
 		if ( '' !== $reference ) {
-			$body .= "\n\n" . sprintf(
+			$referenceLine = "\n\n" . sprintf(
 				/* translators: %s: payment reference code */
 				__( 'Please include this reference with your payment: %s', 'unsupervised-schedular' ),
 				$reference
 			);
 		}
 
-		return (bool) wp_mail( $student->user_email, __( 'Payment due', 'unsupervised-schedular' ), $body );
+		return [
+			'{student_name}' => $studentName,
+			'{items}'        => implode( "\n", $lines ),
+			'{total_due}'    => $currency . ' ' . number_format( $dueTotal, 2 ),
+			'{credit}'       => $credit,
+			'{etransfer}'    => $etransfer,
+			'{reference}'    => $referenceLine,
+		];
 	}
 
 	/**

src/Payment/PaymentEmailController.php

@@ -0,0 +1,144 @@
+<?php
+declare(strict_types=1);
+
+namespace Unsupervised\Schedular\Payment;
+
+use Unsupervised\Schedular\Auth\RoleManager;
+use Unsupervised\Schedular\Val;
+
+/**
+ * Admin screen for viewing and editing the payment-due email template, with a
+ * live preview rendered from sample values. Save is a plain POST (nonce +
+ * capability checked); the preview updates client-side against a REST endpoint
+ * so an admin sees the effect of an edit before saving it.
+ */
+class PaymentEmailController {
+
+	public const NONCE_ACTION = 'usc_payment_email_action';
+
+	public function __construct( private PaymentDueEmailTemplate $template = new PaymentDueEmailTemplate() ) {}
+
+	public function renderPage(): void {
+		if ( ! current_user_can( RoleManager::CAP_MANAGE_BILLING ) ) {
+			wp_die( esc_html__( 'You do not have permission to manage billing settings.', 'unsupervised-schedular' ) );
+		}
+
+		$notice = '';
+		if ( isset( $_POST['usc_action'] ) && check_admin_referer( self::NONCE_ACTION ) ) {
+			// phpcs:ignore WordPress.Security.NonceVerification.Missing -- verified immediately above.
+			$action = sanitize_key( Val::string( wp_unslash( $_POST['usc_action'] ) ) );
+			if ( 'reset' === $action ) {
+				$this->reset();
+				$notice = __( 'Template reset to the built-in default.', 'unsupervised-schedular' );
+			} else {
+				$this->save();
+				$notice = __( 'Payment due email template saved.', 'unsupervised-schedular' );
+			}
+		}
+
+		$subject      = $this->template->subject();
+		$body         = $this->template->body();
+		$itemLine     = $this->template->itemLine();
+		$tokens       = PaymentDueEmailTemplate::tokens();
+		$itemTokens   = PaymentDueEmailTemplate::itemTokens();
+		$previewNonce = wp_create_nonce( 'wp_rest' );
+		$previewUrl   = rest_url( 'us-scheduler/v1/payment-email/preview' );
+
+		// Server-render the initial preview from sample values so the panel is
+		// populated before any JavaScript runs (and if it never does).
+		$preview = self::renderSample( $this->template, $subject, $body, $itemLine );
+
+		include USC_PLUGIN_DIR . 'templates/admin/payment-email.php';
+	}
+
+	/**
+	 * Render the given template text against a fixed set of sample values, using
+	 * the real mailer so the preview matches a genuine scan exactly. The passed
+	 * subject/body/item-line override the stored ones so an unsaved edit can be
+	 * previewed.
+	 *
+	 * @return array{subject: string, body: string}
+	 */
+	public static function renderSample( PaymentDueEmailTemplate $stored, string $subject, string $body, string $itemLine ): array {
+		// A throwaway template returning the supplied (possibly unsaved) text.
+		$draft = new class( $subject, $body, $itemLine ) extends PaymentDueEmailTemplate {
+			public function __construct(
+				private string $draftSubject,
+				private string $draftBody,
+				private string $draftItemLine,
+			) {}
+
+			public function subject(): string {
+				return '' !== $this->draftSubject ? $this->draftSubject : self::defaultSubject();
+			}
+
+			public function body(): string {
+				return '' !== $this->draftBody ? $this->draftBody : self::defaultBody();
+			}
+
+			public function itemLine(): string {
+				return '' !== $this->draftItemLine ? $this->draftItemLine : self::defaultItemLine();
+			}
+		};
+
+		$mailer = new PaymentDueMailer( $draft );
+		$tokens = $mailer->buildTokens( self::sampleStudentName(), self::sampleItems(), self::sampleReference(), self::sampleCredit() );
+
+		return [
+			'subject' => $draft->renderSubject( $tokens ),
+			'body'    => $draft->renderBody( $tokens ),
+		];
+	}
+
+	public static function sampleStudentName(): string {
+		return __( 'Alex Student', 'unsupervised-schedular' );
+	}
+
+	public static function sampleReference(): string {
+		return 'REF12345';
+	}
+
+	public static function sampleCredit(): float {
+		return 20.0;
+	}
+
+	/**
+	 * The sample charges the preview is rendered against — two lessons on
+	 * different dates so the {items} block and grand total are both exercised.
+	 *
+	 * @return list<array{label: string, amount: float, currency: string, due_date: ?string, etransfer_email: ?string}>
+	 */
+	public static function sampleItems(): array {
+		return [
+			[
+				'label'           => __( 'Piano lesson', 'unsupervised-schedular' ),
+				'amount'          => 35.0,
+				'currency'        => 'CAD',
+				'due_date'        => '2026-07-15',
+				'etransfer_email' => '[email protected]',
+			],
+			[
+				'label'           => __( 'Guitar lesson', 'unsupervised-schedular' ),
+				'amount'          => 40.0,
+				'currency'        => 'CAD',
+				'due_date'        => '2026-07-22',
+				'etransfer_email' => '[email protected]',
+			],
+		];
+	}
+
+	private function save(): void {
+		// Nonce is verified by the caller (renderPage) before this method runs.
+		// phpcs:disable WordPress.Security.NonceVerification.Missing
+		$this->template->saveSubject( sanitize_text_field( Val::string( wp_unslash( $_POST['subject'] ?? '' ) ) ) );
+		$this->template->saveBody( sanitize_textarea_field( Val::string( wp_unslash( $_POST['body'] ?? '' ) ) ) );
+		$this->template->saveItemLine( sanitize_text_field( Val::string( wp_unslash( $_POST['item_line'] ?? '' ) ) ) );
+		// phpcs:enable WordPress.Security.NonceVerification.Missing
+	}
+
+	private function reset(): void {
+		$this->template->saveSubject( '' );
+		$this->template->saveBody( '' );
+		$this->template->saveItemLine( '' );
+	}
+}

src/Payment/PaymentEmailPreviewEndpoint.php

@@ -0,0 +1,59 @@
+<?php
+declare(strict_types=1);
+
+namespace Unsupervised\Schedular\Payment;
+
+use Unsupervised\Schedular\Auth\RoleManager;
+use Unsupervised\Schedular\Val;
+
+/**
+ * Renders a live preview of the payment-due email from template text the admin
+ * is editing (not yet saved) against fixed sample values, so the settings screen
+ * can show the resulting email as the admin types. Read-only: it never writes
+ * the template.
+ */
+class PaymentEmailPreviewEndpoint {
+
+	public function __construct( private PaymentDueEmailTemplate $template = new PaymentDueEmailTemplate() ) {}
+
+	/**
+	 * Registers this endpoint's REST routes.
+	 *
+	 * @param non-falsy-string $route_namespace REST namespace the routes are registered under (e.g. `us-scheduler/v1`).
+	 */
+	public function registerRoutes( string $route_namespace ): void {
+		register_rest_route(
+			$route_namespace,
+			'/payment-email/preview',
+			[
+				[
+					'methods'             => \WP_REST_Server::CREATABLE,
+					'callback'            => [ $this, 'preview' ],
+					'permission_callback' => [ $this, 'canManage' ],
+					'args'                => [
+						'subject'   => [ 'type' => 'string' ],
+						'body'      => [ 'type' => 'string' ],
+						'item_line' => [ 'type' => 'string' ],
+					],
+				],
+			]
+		);
+	}
+
+	/**
+	 * Render the submitted (draft) template text against the sample values.
+	 */
+	public function preview( \WP_REST_Request $request ): \WP_REST_Response {
+		$subject  = Val::string( $request->get_param( 'subject' ) );
+		$body     = Val::string( $request->get_param( 'body' ) );
+		$itemLine = Val::string( $request->get_param( 'item_line' ) );
+
+		$rendered = PaymentEmailController::renderSample( $this->template, $subject, $body, $itemLine );
+
+		return new \WP_REST_Response( $rendered, 200 );
+	}
+
+	public function canManage(): bool {
+		return is_user_logged_in() && current_user_can( RoleManager::CAP_MANAGE_BILLING );
+	}
+}

src/RestRegistrar.php

@@ -18,6 +18,7 @@ use Unsupervised\Schedular\Guardian\GuardianService;
 use Unsupervised\Schedular\Offering\BillingModeReconciler;
 use Unsupervised\Schedular\Offering\OfferingEndpoint;
 use Unsupervised\Schedular\Offering\OfferingRepository;
+use Unsupervised\Schedular\Payment\PaymentEmailPreviewEndpoint;
 use Unsupervised\Schedular\Payment\PaymentEndpoint;
 use Unsupervised\Schedular\Payment\PaymentService;
 use Unsupervised\Schedular\Payment\StudioSettings;
@@ -40,15 +41,17 @@ class RestRegistrar {
 	private PolicyEndpoint $policyEndpoint;
 	private EnrollmentEndpoint $enrollmentEndpoint;
 	private PaymentEndpoint $paymentEndpoint;
+	private PaymentEmailPreviewEndpoint $paymentEmailPreviewEndpoint;
 
 	public function __construct( AvailabilityRepository $availability, BookingRepository $bookings, OfferingRepository $offerings, QuestionRepository $questions, PolicyRepository $policies, PolicyVersionRepository $policyVersions, PolicyService $policyService, RegistrationGate $gate, EnrollmentRepository $enrollments, GroupAccessRepository $groupAccess, PaymentService $paymentService, GuardianService $guardians, LessonBooker $booker, BillingModeReconciler $billingModeReconciler ) {
-		$this->availabilityEndpoint = new AvailabilityEndpoint( $availability, new WindowValidator( $offerings ) );
-		$this->bookingEndpoint      = new BookingEndpoint( $availability, $bookings, $offerings, $gate, $paymentService, $booker, new CancellationPolicy( new StudioSettings() ), $guardians, new SessionSchedule( $enrollments, $offerings ) );
-		$this->offeringEndpoint     = new OfferingEndpoint( $offerings, $groupAccess, $billingModeReconciler );
-		$this->questionEndpoint     = new QuestionEndpoint( $questions, $offerings );
-		$this->policyEndpoint       = new PolicyEndpoint( $policies, $policyVersions, $policyService );
-		$this->enrollmentEndpoint   = new EnrollmentEndpoint( $enrollments, $offerings, $gate, $paymentService, $groupAccess, $guardians );
-		$this->paymentEndpoint      = new PaymentEndpoint( $paymentService );
+		$this->availabilityEndpoint        = new AvailabilityEndpoint( $availability, new WindowValidator( $offerings ) );
+		$this->bookingEndpoint             = new BookingEndpoint( $availability, $bookings, $offerings, $gate, $paymentService, $booker, new CancellationPolicy( new StudioSettings() ), $guardians, new SessionSchedule( $enrollments, $offerings ) );
+		$this->offeringEndpoint            = new OfferingEndpoint( $offerings, $groupAccess, $billingModeReconciler );
+		$this->questionEndpoint            = new QuestionEndpoint( $questions, $offerings );
+		$this->policyEndpoint              = new PolicyEndpoint( $policies, $policyVersions, $policyService );
+		$this->enrollmentEndpoint          = new EnrollmentEndpoint( $enrollments, $offerings, $gate, $paymentService, $groupAccess, $guardians );
+		$this->paymentEndpoint             = new PaymentEndpoint( $paymentService );
+		$this->paymentEmailPreviewEndpoint = new PaymentEmailPreviewEndpoint();
 	}
 
 	public function register(): void {
@@ -63,5 +66,6 @@ class RestRegistrar {
 		$this->policyEndpoint->registerRoutes( self::NAMESPACE );
 		$this->enrollmentEndpoint->registerRoutes( self::NAMESPACE );
 		$this->paymentEndpoint->registerRoutes( self::NAMESPACE );
+		$this->paymentEmailPreviewEndpoint->registerRoutes( self::NAMESPACE );
 	}
 }

templates/admin/payment-email.php

@@ -0,0 +1,97 @@
+<?php
+declare(strict_types=1);
+
+if (! defined('ABSPATH')) {
+    exit;
+}
+
+/**
+ * @var string                $subject
+ * @var string                $body
+ * @var string                $itemLine
+ * @var array<string, string> $tokens
+ * @var array<string, string> $itemTokens
+ * @var string                $previewNonce
+ * @var string                $previewUrl
+ * @var array{subject: string, body: string} $preview
+ * @var string                $notice
+ */
+?>
+<div class="wrap">
+    <h1><?php esc_html_e('Payment Due Email', 'unsupervised-schedular'); ?></h1>
+
+    <?php if ('' !== $notice) : ?>
+        <div class="notice notice-success inline">
+            <p><?php echo esc_html($notice); ?></p>
+        </div>
+    <?php endif; ?>
+
+    <p class="description">
+        <?php esc_html_e('This is the email a student receives when the daily billing scan finds payments due for them. Edit the subject and body below, then preview the result with sample values. Leave a field blank to use the built-in default.', 'unsupervised-schedular'); ?>
+    </p>
+
+    <form method="post" id="usc-payment-email-form">
+        <?php wp_nonce_field('usc_payment_email_action'); ?>
+        <input type="hidden" name="usc_action" value="save">
+        <table class="form-table">
+            <tr>
+                <th scope="row"><label for="usc-pe-subject"><?php esc_html_e('Subject', 'unsupervised-schedular'); ?></label></th>
+                <td>
+                    <input type="text" name="subject" id="usc-pe-subject" class="large-text" value="<?php echo esc_attr($subject); ?>">
+                </td>
+            </tr>
+            <tr>
+                <th scope="row"><label for="usc-pe-body"><?php esc_html_e('Body', 'unsupervised-schedular'); ?></label></th>
+                <td>
+                    <textarea name="body" id="usc-pe-body" class="large-text code" rows="10"><?php echo esc_textarea($body); ?></textarea>
+                    <p class="description"><?php esc_html_e('Available tokens:', 'unsupervised-schedular'); ?></p>
+                    <ul>
+                        <?php foreach ($tokens as $token => $description) : ?>
+                            <li><code><?php echo esc_html($token); ?></code> — <?php echo esc_html($description); ?></li>
+                        <?php endforeach; ?>
+                    </ul>
+                </td>
+            </tr>
+            <tr>
+                <th scope="row"><label for="usc-pe-item-line"><?php esc_html_e('Item line', 'unsupervised-schedular'); ?></label></th>
+                <td>
+                    <input type="text" name="item_line" id="usc-pe-item-line" class="large-text code" value="<?php echo esc_attr($itemLine); ?>">
+                    <p class="description"><?php esc_html_e('The template for each charge in the {items} block. Available tokens:', 'unsupervised-schedular'); ?></p>
+                    <ul>
+                        <?php foreach ($itemTokens as $token => $description) : ?>
+                            <li><code><?php echo esc_html($token); ?></code> — <?php echo esc_html($description); ?></li>
+                        <?php endforeach; ?>
+                    </ul>
+                </td>
+            </tr>
+        </table>
+        <?php submit_button(esc_html__('Save Template', 'unsupervised-schedular')); ?>
+    </form>
+
+    <h2><?php esc_html_e('Reset to default', 'unsupervised-schedular'); ?></h2>
+    <p class="description"><?php esc_html_e('Discards your custom subject, body and item line, restoring the built-in default template.', 'unsupervised-schedular'); ?></p>
+    <form method="post" onsubmit="return confirm('<?php echo esc_js(esc_html__('Reset the payment due email to its default template?', 'unsupervised-schedular')); ?>');">
+        <?php wp_nonce_field('usc_payment_email_action'); ?>
+        <input type="hidden" name="usc_action" value="reset">
+        <?php submit_button(esc_html__('Reset to default', 'unsupervised-schedular'), 'delete', 'submit', true); ?>
+    </form>
+
+    <h2><?php esc_html_e('Preview', 'unsupervised-schedular'); ?></h2>
+    <p class="description"><?php esc_html_e('Rendered with sample values. Updates as you edit above.', 'unsupervised-schedular'); ?></p>
+    <table class="form-table">
+        <tr>
+            <th scope="row"><?php esc_html_e('Subject', 'unsupervised-schedular'); ?></th>
+            <td><strong id="usc-pe-preview-subject"><?php echo esc_html($preview['subject']); ?></strong></td>
+        </tr>
+        <tr>
+            <th scope="row"><?php esc_html_e('Body', 'unsupervised-schedular'); ?></th>
+            <td><pre id="usc-pe-preview-body" style="white-space:pre-wrap;background:#fff;border:1px solid #ccd0d4;padding:12px;margin:0;max-width:640px;"><?php echo esc_html($preview['body']); ?></pre></td>
+        </tr>
+    </table>
+</div>
+<script>
+    window.uscPaymentEmailPreview = {
+        url: <?php echo wp_json_encode($previewUrl); ?>,
+        nonce: <?php echo wp_json_encode($previewNonce); ?>
+    };
+</script>

tests/Unit/Payment/PaymentDueEmailTemplateTest.php

@@ -0,0 +1,77 @@
+<?php
+declare(strict_types=1);
+
+namespace Unsupervised\Schedular\Tests\Unit\Payment;
+
+use Brain\Monkey\Functions;
+use Unsupervised\Schedular\Payment\PaymentDueEmailTemplate;
+use Unsupervised\Schedular\Tests\Unit\TestCase;
+
+class PaymentDueEmailTemplateTest extends TestCase
+{
+    public function testFallsBackToDefaultsWhenUnset(): void
+    {
+        Functions\when('get_option')->alias(static fn (string $name, $default = '') => '');
+
+        $template = new PaymentDueEmailTemplate();
+
+        self::assertSame(PaymentDueEmailTemplate::defaultSubject(), $template->subject());
+        self::assertSame(PaymentDueEmailTemplate::defaultBody(), $template->body());
+        self::assertSame(PaymentDueEmailTemplate::defaultItemLine(), $template->itemLine());
+    }
+
+    public function testReadsStoredValues(): void
+    {
+        Functions\when('get_option')->alias(static function (string $name) {
+            return match ($name) {
+                PaymentDueEmailTemplate::OPT_SUBJECT   => 'Custom subject',
+                PaymentDueEmailTemplate::OPT_BODY      => 'Custom body {items}',
+                PaymentDueEmailTemplate::OPT_ITEM_LINE => '{label}: {amount}',
+                default                                => '',
+            };
+        });
+
+        $template = new PaymentDueEmailTemplate();
+
+        self::assertSame('Custom subject', $template->subject());
+        self::assertSame('Custom body {items}', $template->body());
+        self::assertSame('{label}: {amount}', $template->itemLine());
+    }
+
+    public function testRenderSubstitutesTokens(): void
+    {
+        Functions\when('get_option')->alias(static function (string $name) {
+            return match ($name) {
+                PaymentDueEmailTemplate::OPT_SUBJECT => 'Hi {student_name}',
+                PaymentDueEmailTemplate::OPT_BODY    => 'Total: {total_due}',
+                default                              => '',
+            };
+        });
+
+        $template = new PaymentDueEmailTemplate();
+
+        self::assertSame('Hi Sam', $template->renderSubject(['{student_name}' => 'Sam']));
+        self::assertSame('Total: CAD 10.00', $template->renderBody(['{total_due}' => 'CAD 10.00']));
+    }
+
+    public function testSaveWritesOptions(): void
+    {
+        Functions\expect('update_option')->once()->with(PaymentDueEmailTemplate::OPT_SUBJECT, 'S');
+        Functions\expect('update_option')->once()->with(PaymentDueEmailTemplate::OPT_BODY, 'B');
+        Functions\expect('update_option')->once()->with(PaymentDueEmailTemplate::OPT_ITEM_LINE, 'I');
+
+        $template = new PaymentDueEmailTemplate();
+        $template->saveSubject('S');
+        $template->saveBody('B');
+        $template->saveItemLine('I');
+    }
+
+    public function testDefaultBodyCarriesEveryBlockToken(): void
+    {
+        $body = PaymentDueEmailTemplate::defaultBody();
+
+        foreach (['{items}', '{credit}', '{total_due}', '{etransfer}', '{reference}'] as $token) {
+            self::assertStringContainsString($token, $body);
+        }
+    }
+}

tests/Unit/Payment/PaymentDueMailerTest.php

@@ -5,15 +5,27 @@ namespace Unsupervised\Schedular\Tests\Unit\Payment;
 
 use Brain\Monkey\Functions;
 use Mockery;
+use Unsupervised\Schedular\Payment\PaymentDueEmailTemplate;
 use Unsupervised\Schedular\Payment\PaymentDueMailer;
 use Unsupervised\Schedular\Tests\Unit\TestCase;
 
 class PaymentDueMailerTest extends TestCase
 {
-    private function student(string $email): \WP_User
+    protected function setUp(): void
     {
-        $student             = Mockery::mock(\WP_User::class);
-        $student->user_email = $email;
+        parent::setUp();
+
+        // The mailer renders from PaymentDueEmailTemplate, which reads its
+        // subject/body/item-line from options. An empty stored value means the
+        // built-in default template is used — the behaviour these tests assert.
+        Functions\when('get_option')->alias(static fn (string $name, $default = '') => '');
+    }
+
+    private function student(string $email, string $name = 'Alex Student'): \WP_User
+    {
+        $student               = Mockery::mock(\WP_User::class);
+        $student->user_email   = $email;
+        $student->display_name = $name;
 
         return $student;
     }
@@ -129,4 +141,39 @@ class PaymentDueMailerTest extends TestCase
 
         self::assertTrue((new PaymentDueMailer())->send($this->student('[email protected]'), $items));
     }
+
+    public function testRendersCustomTemplateWithTokens(): void
+    {
+        // A stored template overrides the default; tokens are substituted with
+        // the real values gathered from the items and student.
+        Functions\when('get_option')->alias(static function (string $name) {
+            if ($name === PaymentDueEmailTemplate::OPT_SUBJECT) {
+                return 'Hi {student_name} — {total_due}';
+            }
+            if ($name === PaymentDueEmailTemplate::OPT_BODY) {
+                return "Dear {student_name},\n{items}\nOwing: {total_due}";
+            }
+            if ($name === PaymentDueEmailTemplate::OPT_ITEM_LINE) {
+                return '* {label} = {currency} {amount}';
+            }
+            return '';
+        });
+
+        Functions\expect('wp_mail')
+            ->once()
+            ->with(
+                '[email protected]',
+                'Hi Jordan — CAD 35.00',
+                Mockery::on(static function (string $body): bool {
+                    return str_contains($body, 'Dear Jordan,')
+                        && str_contains($body, '* Piano = CAD 35.00')
+                        && str_contains($body, 'Owing: CAD 35.00');
+                })
+            )
+            ->andReturn(true);
+
+        $items = [[ 'label' => 'Piano', 'amount' => 35.0, 'currency' => 'CAD', 'due_date' => '2026-07-15', 'etransfer_email' => null ]];
+
+        self::assertTrue((new PaymentDueMailer())->send($this->student('[email protected]', 'Jordan'), $items));
+    }
 }

tests/Unit/Payment/PaymentEmailControllerTest.php

@@ -0,0 +1,60 @@
+<?php
+declare(strict_types=1);
+
+namespace Unsupervised\Schedular\Tests\Unit\Payment;
+
+use Brain\Monkey\Functions;
+use Unsupervised\Schedular\Payment\PaymentDueEmailTemplate;
+use Unsupervised\Schedular\Payment\PaymentEmailController;
+use Unsupervised\Schedular\Tests\Unit\TestCase;
+
+class PaymentEmailControllerTest extends TestCase
+{
+    protected function setUp(): void
+    {
+        parent::setUp();
+        Functions\when('get_option')->alias(static fn (string $name, $default = '') => '');
+    }
+
+    public function testRenderSampleUsesDefaultTemplateWhenDraftBlank(): void
+    {
+        $stored = new PaymentDueEmailTemplate();
+
+        $rendered = PaymentEmailController::renderSample($stored, '', '', '');
+
+        self::assertSame(PaymentDueEmailTemplate::defaultSubject(), $rendered['subject']);
+        // Default body lists both sample items with a grand total and the sample
+        // reference/credit blocks resolved.
+        self::assertStringContainsString('Piano lesson', $rendered['body']);
+        self::assertStringContainsString('Guitar lesson', $rendered['body']);
+        self::assertStringContainsString('Jul 15, 2026', $rendered['body']);
+        self::assertStringContainsString('Total due: CAD 55.00', $rendered['body']); // 75 - 20 credit
+        self::assertStringContainsString('REF12345', $rendered['body']);
+        self::assertStringContainsString('[email protected]', $rendered['body']);
+    }
+
+    public function testRenderSampleUsesDraftOverStored(): void
+    {
+        $stored = new PaymentDueEmailTemplate();
+
+        $rendered = PaymentEmailController::renderSample(
+            $stored,
+            'Draft: {total_due}',
+            "Hello {student_name}\n{items}",
+            '> {label} {amount}'
+        );
+
+        self::assertSame('Draft: CAD 55.00', $rendered['subject']);
+        self::assertStringContainsString('Hello ' . PaymentEmailController::sampleStudentName(), $rendered['body']);
+        self::assertStringContainsString('> Piano lesson 35.00', $rendered['body']);
+    }
+
+    public function testSampleItemsAreTwoLessons(): void
+    {
+        $items = PaymentEmailController::sampleItems();
+
+        self::assertCount(2, $items);
+        self::assertSame(35.0, $items[0]['amount']);
+        self::assertSame(40.0, $items[1]['amount']);
+    }
+}

tests/Unit/Payment/PaymentEmailPreviewEndpointTest.php

@@ -0,0 +1,59 @@
+<?php
+declare(strict_types=1);
+
+namespace Unsupervised\Schedular\Tests\Unit\Payment;
+
+use Brain\Monkey\Functions;
+use Unsupervised\Schedular\Auth\RoleManager;
+use Unsupervised\Schedular\Payment\PaymentEmailPreviewEndpoint;
+use Unsupervised\Schedular\Tests\Unit\TestCase;
+
+class PaymentEmailPreviewEndpointTest extends TestCase
+{
+    protected function setUp(): void
+    {
+        parent::setUp();
+        Functions\when('get_option')->alias(static fn (string $name, $default = '') => '');
+    }
+
+    public function testPreviewRendersDraftAgainstSampleValues(): void
+    {
+        $endpoint = new PaymentEmailPreviewEndpoint();
+
+        $request = new \WP_REST_Request([
+            'subject'   => 'Draft {total_due}',
+            'body'      => "Hi {student_name}\n{items}",
+            'item_line' => '- {label} {amount}',
+        ]);
+
+        $response = $endpoint->preview($request);
+
+        self::assertInstanceOf(\WP_REST_Response::class, $response);
+        $data = $response->get_data();
+        self::assertSame('Draft CAD 55.00', $data['subject']);
+        self::assertStringContainsString('Piano lesson', $data['body']);
+        self::assertStringContainsString('- Piano lesson 35.00', $data['body']);
+    }
+
+    public function testCanManageRequiresBillingCapability(): void
+    {
+        $endpoint = new PaymentEmailPreviewEndpoint();
+
+        Functions\when('is_user_logged_in')->justReturn(true);
+        Functions\when('current_user_can')->alias(
+            static fn (string $cap): bool => $cap === RoleManager::CAP_MANAGE_BILLING
+        );
+
+        self::assertTrue($endpoint->canManage());
+    }
+
+    public function testCanManageDeniesWithoutCapability(): void
+    {
+        $endpoint = new PaymentEmailPreviewEndpoint();
+
+        Functions\when('is_user_logged_in')->justReturn(true);
+        Functions\when('current_user_can')->justReturn(false);
+
+        self::assertFalse($endpoint->canManage());
+    }
+}

unsupervised-schedular.php

@@ -3,7 +3,7 @@
  * Plugin Name: Unsupervised Scheduler
  * Plugin URI:  https://git.unsupervised.ca/Unsupervised/unsupervised-scheduler
  * Description: Instructor/student lesson scheduling for WordPress.
- * Version:     1.5.8
+ * Version:     1.6.0
  * Requires at least: 6.2
  * Requires PHP: 8.1
  * Author:      Unsupervised
@@ -21,7 +21,7 @@ if (! defined('ABSPATH')) {
     exit;
 }
 
-define('USC_VERSION', '1.5.8');
+define('USC_VERSION', '1.6.0');
 define('USC_PLUGIN_FILE', __FILE__);
 define('USC_PLUGIN_DIR', plugin_dir_path(__FILE__));
 define('USC_PLUGIN_URL', plugin_dir_url(__FILE__));