从 GCM 发送多个通知

我正在使用PHP一次在多个Android设备上发送通知。所有注册ID都是唯一的，以下是我正在发送的CURL请求。

$url='https://android.googleapis.com/gcm/send';
$headers = array(
                'Authorization: key=' . ANDROID_KEY,
                'Content-Type: application/json'
            );
$registration_ids = [];//with multiple registration ids
$notification = array(
                'registration_ids' => $registration_ids,
                'data'             => array('notification_id' => $data['notification_id'],
                                            'title'           => $data['title'],
                                            'message'         => $data['message'])
            );
$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, $url);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLOPT_FRESH_CONNECT, true);
curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, false);
curl_setopt($ch, CURLOPT_POST, true);
curl_setopt($ch, CURLOPT_HTTPHEADER, $headers);
curl_setopt($ch, CURLOPT_POSTFIELDS, json_encode($notification));           
$res = curl_exec($ch);

调试多次后，我无法找到在同一设备上多次通知（超过10次）的任何原因。

有没有办法检查GCM收到的请求的日志。任何线索将不胜感激。