title: Android Firebase phone authentication INVALID_APP_CREDENTIAL:App validation failed
body: <p>I am really new to android firebase and I have implemented the necessary libraries for Firebase Auth. I try putting a valid number, but the log says its:</p>
  
  <pre><code>W/JEJE: onVerificationFailed
  com.google.firebase.FirebaseException: An internal error has occurred. [ INVALID_APP_CREDENTIAL:App validation failed ]
  at com.google.android.gms.internal.nf.zzK(Unknown Source)
  at com.google.android.gms.internal.og.zza(Unknown Source)
  at com.google.android.gms.internal.oh.run(Unknown Source)
  at android.os.Handler.handleCallback(Handler.java:751)
  at android.os.Handler.dispatchMessage(Handler.java:95)
  at android.os.Looper.loop(Looper.java:154)
  at android.app.ActivityThread.main(ActivityThread.java:6176)
  at java.lang.reflect.Method.invoke(Native Method)
  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:888)
  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:778)
  </code></pre>
  
  <p>Here is my code:</p>
  
  <pre><code>public class MainActivity extends AppCompatActivity {
  
      private static String mVerificationId;
      private static PhoneAuthProvider.ForceResendingToken mResendToken;
      private static FirebaseAuth mAuth;
  
  
      @Override
      protected void onCreate(Bundle savedInstanceState) {
          super.onCreate(savedInstanceState);
          setContentView(R.layout.activity_main);
          final EditText editText = (EditText) findViewById(R.id.phone);
          Button submit = (Button) findViewById(R.id.submit);
  
          final PhoneAuthProvider.OnVerificationStateChangedCallbacks mCallBacks = new PhoneAuthProvider.OnVerificationStateChangedCallbacks() {
              @Override
              public void onVerificationCompleted(PhoneAuthCredential phoneAuthCredential) {
                  Log.d("JEJE", "onVerificationCompleted:" + phoneAuthCredential);
  
                  signInWithPhoneAuthCredential(phoneAuthCredential);
              }
  
              @Override
              public void onVerificationFailed(FirebaseException e) {
                  Log.w("JEJE", "onVerificationFailed", e);
  
                  if (e instanceof FirebaseAuthInvalidCredentialsException) {
                      Log.d("JEJE", "INVALID REQUEST");
                  } else if (e instanceof FirebaseTooManyRequestsException) {
                      Log.d("JEJE", "Too many Request");
                  }
              }
  
              @Override
              public void onCodeSent(String s, PhoneAuthProvider.ForceResendingToken forceResendingToken) {
                  super.onCodeSent(s, forceResendingToken);
                  Log.d("JEJE", "onCodeSent:" + s);
  
                  mVerificationId = s;
                  mResendToken = forceResendingToken;
  
              }
          };
  
          submit.setOnClickListener(new View.OnClickListener() {
              @Override
              public void onClick(View v) {
                  String phoneNum = editText.getText().toString();
                  Toast.makeText(MainActivity.this, phoneNum, Toast.LENGTH_SHORT).show();
                  verifyPhone(phoneNum,mCallBacks);
              }
  
          });
      }
  
      private void signInWithPhoneAuthCredential(PhoneAuthCredential phoneAuthCredential) {
          mAuth.signInWithCredential(phoneAuthCredential).addOnCompleteListener(new OnCompleteListener&lt;AuthResult&gt;() {
              @Override
              public void onComplete(@NonNull Task&lt;AuthResult&gt; task) {
                  if (task.isSuccessful()){
                      FirebaseUser user = task.getResult().getUser();
                  }else {
                      if (task.getException() instanceof FirebaseAuthInvalidCredentialsException) {
                          // The verification code entered was invalid
                      }
                  }
              }
          });
      }
  
      public void verifyPhone(String phoneNumber, PhoneAuthProvider.OnVerificationStateChangedCallbacks mCallbacks){
          PhoneAuthProvider.getInstance().verifyPhoneNumber(
                  "+639952874699",        // Phone number to verify
                  60,                 // Timeout duration
                  TimeUnit.SECONDS,   // Unit of timeout
                  this,               // Activity (for callback binding)
                  mCallbacks);        // OnVerificationStateChangedCallback
      }
  
  }
  </code></pre>
  
  <p>please tell me whats wrong thanks..</p>