server/checkout: fix support for fully discounted custom pricing

server/polar/checkout/service.py

@@ -909,26 +909,10 @@ async def handle_stripe_success(
         stripe_price_id = product_price.stripe_price_id
         # For pay-what-you-want prices, we need to generate a dedicated price in Stripe
         if isinstance(product_price, ProductPriceCustom):
-            assert checkout.amount is not None
-            assert checkout.currency is not None
-            assert checkout.product.stripe_product_id is not None
-            price_params: stripe_lib.Price.CreateParams = {
-                "unit_amount": checkout.amount,
-                "currency": checkout.currency,
-                "metadata": {
-                    "product_price_id": str(checkout.product_price_id),
-                },
-            }
-            if product_price.is_recurring:
-                price_params["recurring"] = {
-                    "interval": product_price.recurring_interval.as_literal(),
-                }
-            stripe_custom_price = await stripe_service.create_price_for_product(
-                checkout.product.stripe_product_id,
-                price_params,
-                idempotency_key=f"{idempotency_key}_price",
+            ad_hoc_price = await self._create_ad_hoc_custom_price(
+                checkout, idempotency_key=f"{idempotency_key}_price"
             )
-            stripe_price_id = stripe_custom_price.id
+            stripe_price_id = ad_hoc_price.id
 
         if product_price.is_recurring:
             subscription = checkout.subscription
@@ -1068,6 +1052,13 @@ async def handle_free_success(
         }
         idempotency_key = f"checkout_{checkout.id}"
 
+        # For pay-what-you-want prices, we need to generate a dedicated price in Stripe
+        if isinstance(product_price, ProductPriceCustom):
+            ad_hoc_price = await self._create_ad_hoc_custom_price(
+                checkout, idempotency_key=f"{idempotency_key}_price"
+            )
+            stripe_price_id = ad_hoc_price.id
+
         if product_price.is_recurring:
             (
                 stripe_subscription,
@@ -1676,6 +1667,29 @@ async def _create_or_update_customer(
 
         return customer
 
+    async def _create_ad_hoc_custom_price(
+        self, checkout: Checkout, *, idempotency_key: str
+    ) -> stripe_lib.Price:
+        assert checkout.amount is not None
+        assert checkout.currency is not None
+        assert checkout.product.stripe_product_id is not None
+        price_params: stripe_lib.Price.CreateParams = {
+            "unit_amount": checkout.amount,
+            "currency": checkout.currency,
+            "metadata": {
+                "product_price_id": str(checkout.product_price_id),
+            },
+        }
+        if checkout.product_price.is_recurring:
+            price_params["recurring"] = {
+                "interval": checkout.product_price.recurring_interval.as_literal(),
+            }
+        return await stripe_service.create_price_for_product(
+            checkout.product.stripe_product_id,
+            price_params,
+            idempotency_key=idempotency_key,
+        )
+
     async def _get_eager_loaded_checkout(
         self, session: AsyncSession, checkout_id: uuid.UUID
     ) -> Checkout | None:

server/tests/checkout/test_service.py

@@ -2678,6 +2678,34 @@ async def test_valid_discount_percentage_100(
         stripe_service_mock.set_automatically_charged_subscription.assert_called_once()
         stripe_service_mock.create_out_of_band_invoice.assert_not_called()
 
+    async def test_valid_custom_pricing_discount_percentage_100(
+        self,
+        save_fixture: SaveFixture,
+        stripe_service_mock: MagicMock,
+        session: AsyncSession,
+        product_one_time_custom_price: Product,
+        discount_percentage_100: Discount,
+    ) -> None:
+        checkout = await create_checkout(
+            save_fixture,
+            price=product_one_time_custom_price.prices[0],
+            amount=1000,
+            status=CheckoutStatus.confirmed,
+            discount=discount_percentage_100,
+            payment_processor_metadata={"customer_id": "STRIPE_CUSTOMER_ID"},
+        )
+
+        stripe_service_mock.create_out_of_band_invoice.return_value = SimpleNamespace(
+            id="STRIPE_INVOICE_ID"
+        )
+
+        checkout = await checkout_service.handle_free_success(session, checkout.id)
+
+        assert checkout.status == CheckoutStatus.succeeded
+        stripe_service_mock.create_price_for_product.assert_called_once()
+        stripe_service_mock.create_out_of_band_invoice.assert_called_once()
+        stripe_service_mock.create_out_of_band_subscription.assert_not_called()
+
 
 @pytest.mark.asyncio
 class TestExpireOpenCheckouts: