Firebase stuck at verifying app

Hey all,

I am currently facing an issue with our app implementing firebase. It's stuck at the 4th step:

4. Checking if the app has communicated with our servers. You may need to uninstall and reinstall your app.

I have chosen to skip this step for now and follow these guides:

1. https://docs.microsoft.com/en-us/xamarin/android/data-cloud/google-messaging/remote-notifications-with-fcm?tabs=windows
2. https://docs.microsoft.com/en-us/azure/notification-hubs/xamarin-notification-hubs-push-notifications-android-gcm

I am capable of sending a notification to the specific device and I do receive a firebase registration token. This does work, but somehow when I finish composing the message it won't trigger anything inside my app.

Second of all when sending a message within the azure portal it also receives a message. So the application endpoints seem to connect. (last part of guide 2).

Does someone know why it's not communicating with the servers?

Thanks in advance!