title: Phone Auth not working after signing apk
body: <p>I am creating an app with phoneAuth Firebase, Android. When I was testing it with debug apk it was working but when I signed the apk phone auth is not working
  I used this method to send otp</p>
  
  <pre><code>PhoneAuthProvider.getInstance().verifyPhoneNumber (phone,60,TimeUnit.SECONDS,Register.this,mCallbacks);
  </code></pre>