public function customFieldsCheck() {
        return function () {
            $opts = $this->module->getActingOpts();

            $mes = '';
            if (!usces_is_login()) {
                $mes = usces_filter_customer_check_custom_customer($mes);
            }
            if ($opts['quickpay_custom_delivery_fields'] === 'on') {
                $_POST['delivery']['delivery_flag'] = 1;
                $mes = usces_filter_delivery_check_custom_delivery($mes);
            }
            if ($opts['quickpay_custom_order_fields'] === 'on') {
                $mes = usces_filter_delivery_check_custom_order($mes);
            }
            if (!\WCUtils::is_blank($mes)) {
                return $this->module->errors->getErrorResponse(
                    GenericErrorStore::USCES_CUSTOM_FIELDS_ERR,
                    [$mes],
                    [$mes]
                );
            }
        };
    }