title: Firebase + Proguard/R8
body: <p>I am currently working on setting up Firebase (FCM) in my project and have encountered a problem when I run my R8-obfuscated app, the Firebase service (FirebaseMessagingService) no longer works. Has anyone encountered the same problem? Any solution?</p>
  
  <p><strong>UPD</strong>: Finally I fixed it for FCM by downgrading to</p>
  
  <pre><code>com.google.firebase:firebase-messaging:15.0.0
  </code></pre>
  
  <p>There are some deprecated classes in use now but it works.</p>
  
  <p><strong>UPD2</strong>:
  While running obfuscated app with the newest versions of libraries I also noticed warnings in the logs:</p>
  
  <pre><code>W/FA: Failed to retrieve Firebase Instance Id
  </code></pre>
  
  <p>This is most likely the root of the problem.</p>