title: Subscribe to timeline updates - (400) callbackUrl must be a valid HTTPS URL
body: <p>I've been working with the <a href="https://developers.google.com/glass/develop/mirror/index" rel="nofollow">Mirror API</a>, specifically the <a href="https://developers.google.com/glass/develop/mirror/quickstart/php" rel="nofollow">php quick start</a> project. I'm receiving an error after attempting to subscribe to timeline updates:</p>
  
  <blockquote>
    <p>An error occurred: Error calling POST <a href="https://www.googleapis.com/mirror/v1/subscriptions" rel="nofollow">https://www.googleapis.com/mirror/v1/subscriptions</a>: (400) callbackUrl must be a valid HTTPS URL</p>
  </blockquote>
  
  <p>I do have SSL enabled and working on my test server.</p>
  
  <p>In the <a href="https://developers.google.com/glass/v1/reference/subscriptions/insert" rel="nofollow">subscribe_to_notifications</a> function on mirror-client.php (line 111) I see a reference to the callbackUrl: <code>$subscription-&gt;setCallbackUrl($callback_url);</code></p>
  
  <p>However, I am not able to find where to change this. Should it be set to notify.php? Can someone get me pointed in the right direction?</p>