SMS authentication on android NullPointerException

I'm getting this error

Updated error:

E/AndroidRuntime: FATAL EXCEPTION: main Process: xxx.com.xxx, PID: 4963 java.lang.NullPointerException: Attempt to invoke virtual method 'com.google.android.gms.tasks.Task com.google.android.gms.common.api.GoogleApi.zzb(com.google.android.gms.common.api.internal.zzdf)' on a null object reference at com.google.android.gms.internal.zzdtp.zzb(Unknown Source) at com.google.android.gms.internal.zzdtw.zza(Unknown Source) at com.google.firebase.auth.FirebaseAuth.zza(Unknown Source) at com.google.firebase.auth.PhoneAuthProvider.zza(Unknown Source) at com.google.firebase.auth.PhoneAuthProvider.verifyPhoneNumber(Unknown Source) at xxx.com.xxx.PhoneNumberActivity.onClick(PhoneNumberActivity.java:110) at android.view.View.performClick(View.java:5265) at android.view.View$PerformClick.run(View.java:21534) at android.os.Handler.handleCallback(Handler.java:815) at android.os.Handler.dispatchMessage(Handler.java:104) at android.os.Looper.loop(Looper.java:207) at android.app.ActivityThread.main(ActivityThread.java:5728) at java.lang.reflect.Method.invoke(Native Method) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:789) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:679)

When I try to run this code

PhoneAuthProvider.getInstance().verifyPhoneNumber(
            phoneNumber,        // Phone number to verify
            60,                 // Timeout duration
            TimeUnit.SECONDS,   // Unit of timeout
            this,               // Activity (for callback binding)
            mCallbacks);        // OnVerificationStateChangedCallbacks

In app build.gradle

implementation 'com.google.firebase:firebase-database:11.6.0'
implementation 'com.google.firebase:firebase-auth:11.6.0'

Why is it saying it's null? What is null? I'm running it on android device Android version 6.0. Is it because there's no sim card on the phone? I've already enabled phone authentication in the console and it's working on iOS.

from SMS authentication on android NullPointerException