public function useCoupon() {
        global $usces;

        if (defined('WCEX_COUPON')) {
            $usces->error_message = coupon_check($usces->cart->get_entry());
            if (!empty($usces->error_message)) {
                return json_encode(['error' => $usces->error_message]);
            }
        }

        usces_get_entries();
        (new Fees())->setFees();

        return (new WelcartEntries())->getOrder();
    }