public function updateNotificationIds($id) {
        global $usces;

        if (!in_array($id, $this->ipnNotificationIds, true)) {
            $this->ipnNotificationIds[] = $id;
            $usces->set_order_meta_value(
                self::IPN_NOTIFICATION_IDS,
                json_encode($this->ipnNotificationIds),
                $this->orderid
            );
        }
    }