使用的API接口为https://api.mch.weixin.qq.com/papay/preentrustweb，调用成功后也返回了pre_entrustweb_id。

但是通过官方提供的调用方式：

WXOpenBusinessWebViewReq *req = [[WXOpenBusinessWebViewReq alloc] init];

req.businessType = 12; //固定值

NSMutableDictionary *queryInfoDic = [NSMutableDictionary dictionary];

[queryInfoDic setObject:"pre_entrustweb_id" forKey:"5778aadY9nltAsZzXixCkFIGYnV2V"];

req.queryInfoDic = queryInfoDic;

[WxApi sendReq:req];

却提示mch_id 参数构造错误。