code: protected function getBizContent()
      {
          $content = [
              'body'          => strval($this->body),
              'subject'       => strval($this->subject),
              'out_trade_no'  => strval($this->order_no),
              'total_amount'  => strval($this->amount),
  
              // 销售产品码，商家和支付宝签约的产品码，为固定值QUICK_WAP_PAY
              'product_code'  => 'QUICK_WAP_PAY',
              'goods_type'    => $this->goods_type,
              'passback_params' => $this->return_param,
              // TODO 优惠信息待支持  业务扩展参数，待支持
              // 'promo_params' => '',
              // 'extend_params => '',
              'disable_pay_channels' => $this->limitPay,
              'store_id' => $this->store_id,
              // TODO 在收银台出现返回按钮
              'quit_url' => $this->quit_url,
          ];
  
          $timeExpire = $this->timeout_express;
          if (! empty($timeExpire)) {
              $express = floor(($timeExpire - strtotime($this->timestamp)) / 60);
              ($express > 0) && $content['timeout_express'] = $express . 'm';// 超时时间 统一使用分钟计算
          }
  
          return $content;
      }
docs: 业务请求参数的集合，最大长度不限，除公共参数外所有请求参数都必须放在这个参数中传递
  
  @return string