title: Response does not match challenge, expected value = '727874710', received='727874710'
body: <p>I try to add subscription for realtime update facebook api fanpage.
  I got the error below:</p>
  
  <pre><code>Response does not match challenge, expected value = '727874710', received='727874710'
  </code></pre>
  
  <p>I dont understand what's wrong with it.
  Anyone can suggest me?
  Thanks.</p>