public function request() {
        global $usces;

        $entry = isset($_SESSION['usces_entry']) ? $_SESSION['usces_entry'] : [];
        $order = !empty($entry['order']) ? $entry['order'] : [];

        if (empty($entry) || empty($order)) {
            return $this->module->clientErrorStore->getErrorResponse(ClientErrorStore::INTERNAL_SERVER_ERROR);
        }

        $payload = $this->makeRequestBody();
        $payload = $this->calculateItemPrices($payload);
        $res = $this->module->api->reserve($payload);

        if ($res instanceof GenericError) {
            return $res;
        }

        // add SESSION data of transaction to database for fulfillment on LINE redirect
        add_option(
            $res['info']['transactionId'],
            [
                'acting' => $this->module->getActing(),
                'line_request_res' => $res,
                'total' => $order['total_full_price'],
                'currency' => strtoupper(usces_crcode('return')),
                'capture_now' => $payload['options']['payment']['capture'],
                'usces_cart' => $usces->cart->get_cart(),
                'usces_entry' => isset($_SESSION['usces_entry']) ? $_SESSION['usces_entry'] : [],
                'usces_member' => isset($_SESSION['usces_member']) ? $_SESSION['usces_member'] : [],
            ]
        );

        // save order data preprocessing
        usces_save_order_acting_data($res['info']['transactionId']);

        return $res;
    }