Firebase 401 unauthorized error FCM

Question

I\'m trying to test out Firebase Cloud messaging APIs as all functionality is not available from console (notably customization of notifications when app is in background).

Answer 1

I have the same problem at Server Side Code(C#).

You basically used wrong Server Key (or API Key) for service side code.

Follow below Link over stackoverflow posted by me (Helpful to find Server Key (or API Key) )

FCM (Firebase Cloud Messaging) Push Notification with Asp.Net