diff --git a/server/vbv_lernwelt/shop/tests/test_checkout_api.py b/server/vbv_lernwelt/shop/tests/test_checkout_api.py
index a243ae36..1ec7c52b 100644
--- a/server/vbv_lernwelt/shop/tests/test_checkout_api.py
+++ b/server/vbv_lernwelt/shop/tests/test_checkout_api.py
@@ -11,7 +11,6 @@ from vbv_lernwelt.shop.models import (
     Product,
     VV_PRODUCT_SKU,
 )
-from vbv_lernwelt.shop.services import get_payment_url
 
 USER_USERNAME = "testuser"
 USER_EMAIL = "test@example.com"
@@ -33,8 +32,10 @@ TEST_ADDRESS_DATA = {
     "company_country": "Test Company Country",
 }
 
+REDIRECT_URL = "http://testserver/redirect-url"
 
-class CheckoutAPIView(APITestCase):
+
+class CheckoutAPITestCase(APITestCase):
     def setUp(self) -> None:
         Product.objects.create(
             sku=VV_PRODUCT_SKU,
@@ -53,17 +54,16 @@ class CheckoutAPIView(APITestCase):
         self.client.login(username=USER_USERNAME, password=USER_PASSWORD)
 
     @patch("vbv_lernwelt.shop.views.init_transaction")
-    def test_checkout(self, mock_init_transaction):
+    def test_checkout_happy_case(self, mock_init_transaction):
         # GIVEN
         mock_init_transaction.return_value = "1234567890"
-        redirect_url = "http://testserver/redirect-url"
 
         # WHEN
         response = self.client.post(
             path=reverse("checkout-vv"),
             format="json",
             data={
-                "redirect_url": redirect_url,
+                "redirect_url": REDIRECT_URL,
                 "address": TEST_ADDRESS_DATA,
             },
         )
@@ -71,8 +71,8 @@ class CheckoutAPIView(APITestCase):
         # THEN
         self.assertEqual(response.status_code, status.HTTP_200_OK)
         self.assertEqual(
+            f"https://pay.sandbox.datatrans.com/v1/start/1234567890",
             response.json()["next_step_url"],
-            get_payment_url("1234567890"),
         )
 
         self.assertTrue(
@@ -82,3 +82,38 @@ class CheckoutAPIView(APITestCase):
                 state=CheckoutState.INITIALIZED.value,
             ).exists()
         )
+
+        mock_init_transaction.assert_called_once_with(
+            user=self.user,
+            amount_chf_centimes=300_00,
+            redirect_url_success=f"{REDIRECT_URL}/onboarding/vv/checkout/complete",
+            redirect_url_error=f"{REDIRECT_URL}/onboarding/vv/checkout/address?error",
+            redirect_url_cancel=f"{REDIRECT_URL}/",
+            webhook_url=f"{REDIRECT_URL}/api/shop/transaction/webhook/",
+        )
+
+    @patch("vbv_lernwelt.shop.views.init_transaction")
+    def test_incomplete_setup(self, mock_init_transaction):
+        # GIVEN
+        Product.objects.all().delete()
+        mock_init_transaction.return_value = "1234567890"
+
+        # WHEN
+        response = self.client.post(
+            path=reverse("checkout-vv"),
+            format="json",
+            data={
+                "redirect_url": REDIRECT_URL,
+                "address": TEST_ADDRESS_DATA,
+            },
+        )
+
+        # THEN
+        self.assertEqual(response.status_code, status.HTTP_200_OK)
+
+        expected = (
+            f"{REDIRECT_URL}/onboarding/vv/checkout/address?error&"
+            f"message=vv_product_does_not_exist_needs_to_be_created"
+        )
+
+        self.assertEqual(expected, response.json()["next_step_url"])
diff --git a/server/vbv_lernwelt/shop/tests/test_create_signature.py b/server/vbv_lernwelt/shop/tests/test_create_signature.py
index 1c6892e5..ac7297d6 100644
--- a/server/vbv_lernwelt/shop/tests/test_create_signature.py
+++ b/server/vbv_lernwelt/shop/tests/test_create_signature.py
@@ -3,7 +3,7 @@ from unittest import TestCase
 from vbv_lernwelt.shop.services import is_signature_valid
 
 
-class DatatransWebhookSigning(TestCase):
+class DatatransWebhookSigningTestCase(TestCase):
     # Key is from their example in the docs, not ours! :D
     HMAC_KEY_FROM_THE_DOCS_NOT_HAZARDOUS = (
         "861bbfc01e089259091927d6ad7f71c8"
diff --git a/server/vbv_lernwelt/shop/views.py b/server/vbv_lernwelt/shop/views.py
index ee6df6eb..0a5496b3 100644
--- a/server/vbv_lernwelt/shop/views.py
+++ b/server/vbv_lernwelt/shop/views.py
@@ -107,12 +107,18 @@ def checkout_vv(request):
     """
     sku = VV_PRODUCT_SKU
     logger.info(f"Checkout requested: sku={sku}", user_id=request.user.id)
+    base_redirect_url = request.data["redirect_url"]
 
     try:
         product = Product.objects.get(sku=sku)
     except Product.DoesNotExist:
-        raise Exception(
-            f"Required Product not found: {sku} must be created in the admin interface first.",
+        return JsonResponse(
+            {
+                "next_step_url": checkout_error_url(
+                    base_url=base_redirect_url,
+                    message="vv_product_does_not_exist_needs_to_be_created",
+                )
+            },
         )
 
     checkouts = CheckoutInformation.objects.filter(
@@ -131,7 +137,6 @@ def checkout_vv(request):
         return JsonResponse({"next_step_url": get_payment_url(checkout.transaction_id)})
 
     # not yet initialized at all, or canceled/failed
-    base_redirect_url = request.data["redirect_url"]
     transaction_id = init_transaction(
         user=request.user,
         amount_chf_centimes=product.price,
@@ -162,8 +167,13 @@ def webhook_url(base_url: str) -> str:
     return f"{base_url}/api/shop/transaction/webhook/"
 
 
-def checkout_error_url(base_url: str) -> str:
-    return f"{base_url}/onboarding/vv/checkout/address?error"
+def checkout_error_url(base_url: str, message: str | None = None) -> str:
+    url = f"{base_url}/onboarding/vv/checkout/address?error"
+
+    if message:
+        url += f"&message={message}"
+
+    return url
 
 
 def checkout_cancel_url(base_url: str) -> str: