Default FirebaseApp is not initialized in this process. Make sure to call FirebaseApp.initializeApp(Context) first

For me, none of the solutions worked that were given anywhere. Only this worked. Just had to downgrade my google services from 4.1.0 to 4.0.0

dependencies {
    classpath 'com.android.tools.build:gradle:3.3.0-alpha08'
    classpath 'com.google.gms:google-services:4.0.0'
    /*classpath 'com.google.gms:google-services:4.1.0' <-- this was the problem */
}

So if you have updated the google services, just try to downgrade or change to an older version. Hope it helps

Add the plugin to the build.gradle (app level)

// ADD THIS AT THE BOTTOM

apply plugin: 'com.google.gms.google-services'

Make sure:

1. Package name in AndroidManifest.xml is identical to one in the google-services.json
2. google-services.json build action is set to GoogleServicesJson
3. After step 2 restart your IDE & clean & rebuild
4. Explicitly call FirebaseApp.InitializeApp(Application.Context); in MainActivity.OnCreate just before the LoadApplication(..)