public function sendNotification($scope, $event, $nid = null, $theme = null, $timestamp = null, $uid = null)
    {
        if ($this->connector->getURL() === null) {
            return 'Cannot find site URL from configuration.';
        }
        $url = $this->connector->getURL().self::VERSION.'/notification';
        $params = [
            'scope' => $scope,
            'event' => $event,
            'nid' => $nid,
            'theme' => $theme,
            'timestamp' => $timestamp,
            'uid' => $uid,
        ];
        $response = $this->connector->connecting($url, $params, 'POST');
        if (isset($response->notification)) {
            return $response->message;
        }

        return $response;
    }