code: public function refund($options = [])
      {
          $this->config = array_merge($this->config, $options);
          $this->config['op_user_id'] = isset($this->config['op_user_id']) ?: $this->userConfig->get('mch_id', '');
          $this->unsetTradeTypeAndNotifyUrl();
          return $this->getResult($this->gateway_refund, true);
      }
docs: 订单退款操作
  @param array $options
  @return array
  @throws GatewayException