Migrate GCM to FCM
If you still have a GCM (Google Cloud Messaging) setup for managing Android or Chrome devices, it needs to be migrated to a FCM (Firebase Cloud Messaging) account. GCM is end of life and Google is disabling it in the second quarter 2019.
The instructions in this section assume that you are adding Firebase to an existing Google Cloud project for GCM. If you already have an existing Firebase project into which you would like to migrate a GCM app and its users, see Migrate GCM to an existing Firebase project for important alternative instructions.
- In the Firebase console, select Add Project.
- Select your GCM project from the list of existing Google Cloud projects, and select Add Firebase.
- In the Firebase welcome screen, select Add Firebase to your Android App.
- Provide your package name and SHA-1, and select Add App. A new google-services.json file for your Firebase app is downloaded.
- Select Continue and follow the detailed instructions for adding the Google Services plugin in Android Studio.
Taken from: https://developers.google.com/cloud-messaging/android/android-migrate-fcm
You need to handle 1.1 - 1.5
FileWave has handled 2-5