diff --git a/chat/server.js b/chat/server.js
index 0a2983b..9e157e3 100644
--- a/chat/server.js
+++ b/chat/server.js
@@ -13341,6 +13341,11 @@ async function handleAdminTopupCheckout(req, res) {
     const returnUrl = `${resolveBaseUrl(req)}/test-checkout`;
     const orderId = `admin_test_topup_${randomUUID()}`;
 
+    // Helper to validate email format
+    const isValidEmail = (email) => /^[^\s@]+@[^\s@]+\.[^\s@]+$/.test(String(email || ''));
+    const customerEmail = customer.email || ADMIN_USER || '';
+    const validEmail = isValidEmail(customerEmail) ? customerEmail : 'admin@example.com';
+
     const checkoutBody = {
       product_cart: [{
         product_id: pack.productId,
@@ -13348,7 +13353,7 @@ async function handleAdminTopupCheckout(req, res) {
         amount: unitAmount,
       }],
       customer: {
-        email: (customer.email || ADMIN_USER || 'admin@example.com'),
+        email: validEmail,
         name: (customer.name || ADMIN_USER || 'Admin'),
       },
       metadata: {