From 2d87428c1194e88a50433f8e58f978e5cfb13344 Mon Sep 17 00:00:00 2001
From: Thomas Kaul <4159106+dtslvr@users.noreply.github.com>
Date: Thu, 15 Oct 2026 11:47:10 +0200
Subject: [PATCH] Fix type check of unsupported language codes in Stripe
 checkout session

---
 apps/api/src/app/subscription/subscription.service.ts      | 4 +++-
 apps/api/src/app/subscription/types/string-literal.type.ts | 7 +++++++
 2 files changed, 10 insertions(+), 1 deletion(-)
 create mode 100644 apps/api/src/app/subscription/types/string-literal.type.ts

diff --git a/apps/api/src/app/subscription/subscription.service.ts b/apps/api/src/app/subscription/subscription.service.ts
index b46d385432..143f89950b 100644
--- a/apps/api/src/app/subscription/subscription.service.ts
+++ b/apps/api/src/app/subscription/subscription.service.ts
@@ -23,6 +23,8 @@ import { addMilliseconds, isBefore } from 'date-fns';
 import ms, { StringValue } from 'ms';
 import Stripe from 'stripe';
 
+import { StringLiteral } from './types/string-literal.type';
+
 @Injectable()
 export class SubscriptionService {
   private readonly logger = new Logger(SubscriptionService.name);
@@ -268,7 +270,7 @@ export class SubscriptionService {
     const unsupportedLanguageCodes: Record<
       Exclude<
         (typeof SUPPORTED_LANGUAGE_CODES)[number],
-        Stripe.Checkout.SessionCreateParams.Locale
+        StringLiteral<Stripe.Checkout.SessionCreateParams.Locale>
       >,
       true
     > = {
diff --git a/apps/api/src/app/subscription/types/string-literal.type.ts b/apps/api/src/app/subscription/types/string-literal.type.ts
new file mode 100644
index 0000000000..1f25cb81a4
--- /dev/null
+++ b/apps/api/src/app/subscription/types/string-literal.type.ts
@@ -0,0 +1,7 @@
+// Removes the open string type (e.g. OtherString of Stripe), which matches
+// every string, and keeps only the string literals
+export type StringLiteral<T> = T extends string
+  ? string extends T
+    ? never
+    : T
+  : never;