code: private function __setHeaders($ch)
      {
          curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
          curl_setopt($ch, CURLOPT_HTTPHEADER, array(
              'User-Agent: ' . $this->api->getUserAgentHeader(),
          ));
      }
docs: Set all the headers for request and set return transfer.
  
  @param resource $ch. Curl resource.
  @return void