private function sendCallback(NotificationInterface $notification, ObjectManager $om)
 {
     if ($notification->getCallbackUrl()) {
         $secret = $notification->getCategory()->getClient()->getSecret();
         $base['data'] = json_encode(array('id' => $notification->getId(), 'person_id' => $notification->getPerson()->getId(), 'read_date' => $notification->getReadDate()->getTimestamp()));
         $base['signature'] = hash_hmac('sha256', $base['data'], $secret);
         $dataPost = http_build_query($base);
         curl_setopt($this->ch, CURLOPT_URL, $notification->getCallbackUrl());
         curl_setopt($this->ch, CURLOPT_POST, 1);
         curl_setopt($this->ch, CURLOPT_POSTFIELDS, $dataPost);
         $curlResponse = curl_exec($this->ch);
         $code = curl_getinfo($this->ch, CURLINFO_HTTP_CODE);
         if ($code != '200') {
             $this->registerFailedCallback($notification, $om, $this->ch, $curlResponse);
         }
     }
 }