FA PHONE SignInWithAuthCredentials

        //used for signing the user
        private void signInWithPhoneAuthCredential(PhoneAuthCredential credential) {
            mAuth.signInWithCredential(credential)
                    .addOnCompleteListener(VerifyPhoneActivity.this,
                            new OnCompleteListener<AuthResult>() {

                        @Override
                        public void onComplete(@NonNull Task<AuthResult> task) {
                            if (task.isSuccessful()) {
                                //verification successful we will start the profile activity
                                Intent intent = new Intent(VerifyPhoneActivity.this, ProfileActivity.class);
                                intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK | Intent.FLAG_ACTIVITY_CLEAR_TASK);
                                startActivity(intent);

                            } else {

                                //verification unsuccessful.. display an error message

                                String message = "Somthing is wrong, we will fix it soon...";

                                if (task.getException() instanceof FirebaseAuthInvalidCredentialsException) {
                                    message = "Invalid code entered...";
                                }
                                Toast.makeText(VerifyPhoneActivity.this,message,Toast.LENGTH_SHORT).show();
                            }
                        }
                    });
        }