title: Flutter firebase auth phone authentication fails even with test numbers
body: <p>I am using the firebase_auth package to enable phone authentication in my flutter app. I followed firebase-flutter tutorial and set up firebase project and an app with android support.</p>
  
  <p>I then created my login page by following the firebase_auth example code, but I am getting the following error with sample number/code provided in example</p>
  
  <pre><code>PlatformException(error, Cannot create PhoneAuthCredential without either verificationProof, sessionInfo, ortemprary proof., null)
  </code></pre>
  
  <p>When I try verifyPhoneNumber, the following error is printed in text widget below</p>
  
  <pre><code>Phone authentication failed: Network error
  </code></pre>
  
  <p>.. and my network is all fine.</p>