title: Error 403: Error sending test message to Cloud PubSub: User not authorized to perform this action
body: <p>I want to set up a push notification watch but I receive an error response. What authorization I need?</p>
  
  <p>Request:</p>
  
  <pre><code>// Google API
  $client = getClient();
  
  // POST request    
  $ch = curl_init('https://www.googleapis.com/gmail/v1/users/me/watch');
  
  curl_setopt_array($ch, array(
      CURLOPT_POST =&gt; TRUE,
      CURLOPT_RETURNTRANSFER =&gt; TRUE,
      CURLOPT_HTTPHEADER =&gt; array(
          'Authorization: Bearer ' . $client-&gt;getAccessToken()['access_token'],
          'Content-Type: application/json'
      ),
      CURLOPT_POSTFIELDS =&gt; json_encode(array(
          'topicName' =&gt; 'projects/xxxx/topics/xxxx',
          'labelIds' =&gt; ["INBOX"]
      ))
  ));
  </code></pre>
  
  <p>Response:</p>
  
  <pre><code>{
   "error": {
    "errors": [
     {
      "domain": "global",
      "reason": "forbidden",
      "message": "Error sending test message to Cloud PubSub projects/xxxx/topics/xxxx : User not authorized to perform this action."
     }
    ],
    "code": 403,
    "message": "Error sending test message to Cloud PubSub projects/xxxx/topics/xxxx : User not authorized to perform this action."
   }
  }
  </code></pre>
  
  <p>More details:</p>
  
  <ul>
  <li>The scope used is <code>GMAIL_READONLY</code>. </li>
  <li>The suscription and the topic exist and they were created in the same console. </li>
  <li>I tried to publish a new message from the console and it has worked.</li>
  </ul>