title: Flutter cloud_firestore persistence is not working even if it is enabled
body: <p>I've done tons of searches on this. But, my flutter app is working nice on the active network. I've enabled persistence for cloud_firestore, but it's showing this error:</p>
  <pre><code>[cloud_firestore/unavailable] The service is currently unavailable. This is a most likely a transient condition and may be corrected by retrying with a backoff.
  </code></pre>
  <p>My sample code:</p>
  <pre><code>FirebaseFirestore db = FirebaseFirestore.instance;
    db.settings = Settings(persistenceEnabled: true, cacheSizeBytes: 10000000);
  
  final ref = db.doc(&quot;some_collection/some_doc&quot;);
  
  try{
    ref.update({&quot;key&quot;: value});
  } catch(error) {
    print(error.toString());
  }
  </code></pre>
  <p>My <code>pubspec.yaml</code>:</p>
  <pre><code>firebase_messaging: ^8.0.0-dev.14
  firebase_core: ^0.7.0
  firebase_auth: ^0.20.0+1
  flutter_local_notifications: ^3.0.3
  cloud_firestore: ^0.16.0
  </code></pre>