微信企业号 上传媒体图片 时 media 怎么写 （c#）

求上传图片的代码
string strToken = "vy3OOc0Ci1XRJjnPmXLY9pkpZqjKPb0xm1ul5do7AruZpinM0gAHLtLkX1Z_Vvcj";
string msgtype = "image";
string filename="10.jpg";
//上传图片获取media_id
string filepath = HttpContext.Current.Server.MapPath("10.jpg");

        string mssead = "{\"media\":\"@" + filepath + "\",\"filename\":\"" + filename + "\"}";
        string url ="https://qyapi.weixin.qq.com/cgi-bin/media/upload?access_token="+strToken+"&type="+msgtype+"";
        string result = PXTHttpUtility.Post(url, mssead, MyOnRequestComplete);

老是报410005 错误 求解？