Server key authentication has been deprecated by Google ([Source](https://web.archive.org/web/20260108211426/https://firebase.google.com/docs/cloud-messaging/migrate-v1#update-authorization-of-send-requests)). Using the Instance ID API fails with the following errors. ``` FCM: Unexpected error: '{"error": "Authenticating using server key is deprecated. Please use an OAuth2 token instead."}' ```
Server key authentication has been deprecated by Google (Source).
Using the Instance ID API fails with the following errors.