public function customFieldsGet($entity, $code)
    {
        if (empty($code)) {
            throw new \InvalidArgumentException(
                'Parameter `code` must be not empty'
            );
        }

        if (empty($entity) || !in_array($entity, ['customer', 'order'])) {
            throw new \InvalidArgumentException(
                'Parameter `entity` must contain a data & value must be `order` or `customer`'
            );
        }

        /* @noinspection PhpUndefinedMethodInspection */
        return $this->client->makeRequest(
            "/custom-fields/$entity/$code",
            "GET"
        );
    }