Class file for com.google.android.gms.internal.zzaja not found

Question

I am using Fragment for the designing of the Firebase simple login registration.

I get error in the OnCreateView() method on initializing

Answer 1

Do not mix 12 and 15, use this

implementation 'com.google.firebase:firebase-core:16.0.0'
implementation 'com.google.firebase:firebase-auth:16.0.1'
implementation 'com.google.firebase:firebase-messaging:17.0.0'