参照文档：https://pay.weixin.qq.com/wiki/doc/apiv3/wxpay/pay/combine/chapter3_2.shtml

API返回结果：{ code: 'PARAM_ERROR', message: '受理机构必须传入sub_mch_id' }

1、开发文档中并没有接口返回的：sub_mch_id参数，所有必填参数都是填了的，接口却一直报这个错误

2、烦请问一下子单商户号和二级商户号有什么不一样的吗？子单商户号是从哪里来的？

请求报文：{

    "combine_appid":"服务商appid",

    "combine_mchid":"服务商mchid",

    "combine_out_trade_no":"订单号",

    "sub_orders":[

        {

            "mchid":"特约商户machid",

            "attach":"95",

            "amount":{

                "total_amount":1,

                "currency":"CNY"

            },

            "out_trade_no":"子订单号xxxx",

            "sub_mchid":"特约商户machid",

            "profit_sharing":true,

            "description":"商品购买",

            "settle_info":{

                "profit_sharing":true

            }

        }

    ],

    "combine_payer_info":{

        "openid":"用户openid"

    },

    "notify_url":"回调地址"

}