title: Facebook Requests Dialog: Sending Requests Failed
body: <p>I just copy the source codes from <a href="https://developers.facebook.com/docs/reference/dialogs/requests/">https://developers.facebook.com/docs/reference/dialogs/requests/</a>, JavaScript Example section, change to my API ID, then I can see the Dialog.
  but when I sent a Request to One or More Users, I always got the error:</p>
  
  <p>An error occurred with xxxx. Please try again later.</p>
  
  <p>API Error Code: 2
   API Error Description: Service temporarily unavailable
   Error Message: User can't send this request: Unknown error</p>
  
  <p>Did anyone encountered this before?</p>