Newbe Dev Stack

Answer : Yeah GoogleApiClient has been deprecated. As per the documentation: When you want to make a call to one of the Google APIs provided in the Google Play services library (such as Google Sign-in and Drive), you need to create an instance of one the API client objects, which are subclasses of GoogleApi Particularly for the authentication api, you now need to use GoogleSignInClient . // Configure sign-in to request the user's ID, email address, and basic // profile. ID and basic profile are included in DEFAULT_SIGN_IN. GoogleSignInOptions gso = new GoogleSignInOptions.Builder(GoogleSignInOptions.DEFAULT_SIGN_IN) .requestEmail() .build(); // Build a GoogleSignInClient with the options specified by gso. mGoogleSignInClient = GoogleSignIn.getClient(this, gso); You may refer following documentations for more details: Integrating Google Sign-In into Your Android App Moving Past GoogleApiClient

Answer : In my case, I have my number on Phone numbers for testing (optional) Removing it from there, firebase started sending SMS Code to my number. Spark Plan offer 10k phone auth per month. So that you can test and deploy your app without paying a penny. In case someone is not getting the concept or reason of not sent sms again then please go through on my below details. I have been confused for very long time that why I didn't get sms for second time, third and so on.. First Read the original documentation: onVerificationCompleted(PhoneAuthCredential) This method is called in two situations: Instant verification: in some cases the phone number can be instantly verified without needing to send or enter a verification code. Auto-retrieval: on some devices, Google Play services can automatically detect the incoming verification SMS and perform verification without user action. (This capability might be unavailable with some carriers.) ...

Answer : Your second approach is close, you just need to use <GetTokenResult> instead of <UploadTask.TaskSnapshot> as that is for uploading images using Firebase Storage. Try this: user.getIdToken(true).addOnSuccessListener(new OnSuccessListener<GetTokenResult>() { @Override public void onSuccess(GetTokenResult result) { String idToken = result.getToken(); //Do whatever Log.d(TAG, "GetTokenResult result = " + idToken); } });