title: The caller does not have permission to execute the specified operation
body: <p>I am trying to build an app that contains chat, but the error message appears:</p>
  <blockquote>
  <p>[ERROR:flutter/lib/ui/ui_dart_state.cc(186)] Unhandled Exception: [cloud_firestore/permission-denied] The caller does not have permission to execute the specified operation.</p>
  </blockquote>
  <p>My firebase rules:</p>
  <pre><code>rules_version = '2';
  service cloud.firestore {
    match /databases/{database}/documents {
    
  match /users/{uid}{
  allow write: if request.auth != null &amp;&amp; request.auth.uid == uid;
  }
  
  match /users/{uid}{
  allow read: if request.auth != null;
  }
  
  match /chat/{document=**}{
      allow read: if request.auth != null;
      }
    }
  }
  </code></pre>
  <p><a href="https://i.stack.imgur.com/VS4Bv.png" rel="nofollow noreferrer">enter image description here</a></p>
  <p>as seen in the picture above, when I write a message and send it, it doesn't appear in the screen, and the error message is written in terminal</p>