diff --git a/src/lib/payments.functions.ts b/src/lib/payments.functions.ts
index f274b17..dbca942 100644
--- a/src/lib/payments.functions.ts
+++ b/src/lib/payments.functions.ts
@@ -189,3 +189,65 @@ export const getPublicPaymentRequest = createServerFn({ method: "GET" })
     if (!row) throw new Error("Payment request not found");
     return row;
   });
+
+// Public: always creates a fresh Stripe Checkout session for the pay page.
+// Old stripe_checkout_url values become invalid when the Stripe key is
+// rotated or after 24h, so we never reuse the stored URL on click.
+export const startPublicCheckout = createServerFn({ method: "POST" })
+  .inputValidator((data: { id: string }) => data)
+  .handler(async ({ data }) => {
+    const { supabaseAdmin } = await import("@/integrations/supabase/client.server");
+    const { data: row, error } = await supabaseAdmin
+      .from("payment_requests")
+      .select("*")
+      .eq("id", data.id)
+      .maybeSingle();
+    if (error || !row) throw new Error("Payment request not found");
+    if (row.status === "paid") throw new Error("This payment has already been paid");
+    if (row.status === "canceled") throw new Error("This payment request was canceled");
+
+    const stripe = getStripe();
+    const origin = getOrigin();
+    const successUrl = `${origin}/pay/${row.id}?status=success`;
+    const cancelUrl = `${origin}/pay/${row.id}?status=cancel`;
+
+    const session = await stripe.checkout.sessions.create({
+      mode: "payment",
+      payment_method_types: ["card"],
+      customer_email: row.recipient_email || undefined,
+      line_items: [
+        {
+          price_data: {
+            currency: "usd",
+            unit_amount: row.base_amount_cents,
+            product_data: {
+              name: row.description || `Payment from ${row.recipient_name}`,
+            },
+          },
+          quantity: 1,
+        },
+        {
+          price_data: {
+            currency: "usd",
+            unit_amount: row.fee_amount_cents,
+            product_data: { name: "Processing fee (2.9% + $0.30)" },
+          },
+          quantity: 1,
+        },
+      ],
+      success_url: successUrl,
+      cancel_url: cancelUrl,
+      metadata: { payment_request_id: row.id },
+    });
+
+    await supabaseAdmin
+      .from("payment_requests")
+      .update({
+        stripe_session_id: session.id,
+        stripe_checkout_url: session.url ?? null,
+      })
+      .eq("id", row.id);
+
+    if (!session.url) throw new Error("Stripe did not return a checkout URL");
+    return { checkout_url: session.url };
+  });