I have implemented Firebase for cloud messaging :
https://firebase.google.com/docs/cloud-messaging/android/client#sample-register
I have follow all the steps but FirebaseInstanceIdService.onTokenRefresh is never called.
the only message from firebase on the log is :
FirebaseInitProvider: FirebaseApp initialization unsuccessful
Setup the firebase sdk and generate a google-services.json and include it in your project. As described in this guide.