PhoneAuthProvider.OnVerificationStateChangedCallbacks callbacks
        = new PhoneAuthProvider.OnVerificationStateChangedCallbacks() {
    @Override
    public void onVerificationCompleted(PhoneAuthCredential credential) {
        Log.d(TAG, "onVerificationCompleted:" + credential);
        MobileVerification.credential = credential;
        openOTPvalidation(ON_VERIFICATION);
    }

    @Override
    public void onVerificationFailed(FirebaseException e) {
        postException(context, TAG, e);
    }

    @Override
    public void onCodeSent(String s, PhoneAuthProvider.ForceResendingToken token) {
        super.onCodeSent(s, token);
        verificationCode    = s;
        forceResendingToken = token;
        openOTPvalidation(OTP_SEND);
    }
};

private void getOTP() {
    if (activity != null) {
        pDialog = SupportingMethods.showDialogLoading(activity);
        pDialog.show();
    }
    String mobile   = "+91" + mob;
    PhoneAuthProvider.getInstance().verifyPhoneNumber(
            mobile,        // Phone number to verify
            60,                 // Timeout duration
            TimeUnit.SECONDS,   // Unit of timeout
            activity,               // Activity (for callback binding)
            callbacks);        // OnVerificationStateChangedCallbacks
}

com.google.firebase.auth.FirebaseAuthException: This app is not authorized to use Firebase Authentication. Please verifythat the correct package name and SHA-1 are configured in the Firebase Console. [ App validation failed ]
        at com.google.firebase.auth.api.internal.zzdr.zzb(Unknown Source)
        at com.google.firebase.auth.api.internal.zzet.zza(Unknown Source)
        at com.google.firebase.auth.api.internal.zzew.run(Unknown Source)
        at android.os.Handler.handleCallback(Handler.java:739)
        at android.os.Handler.dispatchMessage(Handler.java:95)
        at android.os.Looper.loop(Looper.java:160)
        at android.app.ActivityThread.main(ActivityThread.java:5541)
        at java.lang.reflect.Method.invoke(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:372)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:964)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:759)
        ************ DEVICE INFORMATION ***********
        Brand: OPPO
        Device: A37f
        Model: A37fw
        Id: LMY47V
        Product: A37fw