来自Facebook的实时页面更新

Question

I have a web application which needs to fetch the real time updates to a particular page. I have gone through a lot of questions on this forums and yet not found anything that works for me. When I subscribe to the page updates

I am supplying valid app_id, app_secret and app_url.

 <?php

  $app_id = '';
  $app_secret = '';
  $app_url = '';
  $fields = 'feed';
  $verify_token = 'abcd@123';

  // Fetching an App Token
  $app_token_url = 'https://graph.facebook.com/oauth/access_token?client_id='
                   .$app_id.'&client_secret='.$app_secret
                   .'&grant_type=client_credentials';
  $ch = curl_init();
  curl_setopt($ch, CURLOPT_URL, $app_token_url);
  curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
  $res = curl_exec($ch);
  parse_str($res, $token);

  if (isset($token['access_token'])) {
    // Let's register a callback
    $params = array(
      'object'
        =>  'page',
      'fields'
        =>  $fields,
      'callback_url'
        // This is the endpoint that will be called when
        // a User updates the location field
        =>  $app_url . '/index.php?action=callback',
      'verify_token'
        =>  $verify_token,
    );

    curl_setopt($ch, CURLOPT_URL, 'https://graph.facebook.com/'
                                  .$app_id.'/subscriptions?access_token='
                                  .$token['access_token']);
    curl_setopt($ch, CURLOPT_POST, 1);
    curl_setopt($ch, CURLOPT_POSTFIELDS, $params);
    $res = curl_exec($ch);
    if ($res && $res != 'null') {
      print_r($res);
    }

    // Fetch list of all callbacks
    curl_setopt($ch, CURLOPT_POST, 0);
    $res = curl_exec($ch);
  }
  if ($res && $res != 'null') {
    print_r($res);
    error_log('updates = ' . print_r($res, true));
  }
  curl_close($ch);

?>

the FB posts to my callback URL but doesn't send the id of the post which was updated, instead it sends the user id in both the id as well as the uid. Even the updates are irregular, sometimes there is a notification, at other times no notification.

What do I need to do make this work?

1. There is something about whitelisting apps -- does that need to be done.
2. Do I need to make this app as a facebook app and have the page install this app on a tab?
3. Do I need special permission to be granted by the page admin.
4. Can this be done at all?

Any help would be very welcome. Thanks!!

A similar question on this forum :Facebook Real Time Update return only "changed_fields":["feed"] and not the actual comment