Hi Izidora,
It looks like you’ve set up most of the configuration correctly, but the error "The Push Notification System rejected the request because of an invalid credential" suggests an issue with authentication. Here are some key things you should check
verify the credential which you have given like private key, client email id and project id is you entered in the Azure Notification Hub match exactly with the values in the JSON file you downloaded from the Firebase Console, also check the private key is entered correctly without extra spaces or line breaks.
check service account which you have created have necessary permissions
steps like:
Go to Google Cloud Console → IAM & Admin → IAM.
Find the service account associated with your JSON key.
The role "Firebase Service Management Service Agent" should be sufficient, but you might also want to check that it has the "Firebase Admin" role or similar permissions.
Also check Firebase service management is enable if not try to enable it
After updating the credentials in the Azure portal, it may take a few minutes for the changes to propagate. If you just made the changes, try waiting a bit and then test again.
double-check for any typos in the credentials you entered. Even a small mistake can lead to authentication failures.
https://learn.microsoft.com/en-us/azure/notification-hubs/firebase-migration-rest#rest-api
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