c# POST 500错误 JS可以跑通

asp.net C# 跑POST服务器报500错误~ 用JS可以跑通。 帮忙看下C#段怎么改

function getIscToken(){
    var id='1122'; 
    var code='3344';
    var sURL="https://*******";
    var _data = {"appId":id,"CODE":code};
    $.ajax({
        type:"post",
        data:JSON.stringify(_data),
        contentType:"application/json;charset=utf-8",
        url: sURL,
        dataType:"json",
        success:function(res){
            daa=res.data;
            $("#st_area").html(daa);
        }
    });
}

        string _url = "https://*****";
        string jsonParam = "{appId:1122,CODE:3344}";
        var request = (HttpWebRequest)WebRequest.Create(_url);
        request.Method = "POST";
        request.ContentType = "application/json";
       
        byte[] byteData = Encoding.UTF8.GetBytes(jsonParam);
        int length = byteData.Length; 
        request.ContentLength = length;
        Stream writer = request.GetRequestStream();
        writer.Write(byteData, 0, length);
        writer.Close();

        var response = (HttpWebResponse)request.GetResponse();
        var responseString = new StreamReader(response.GetResponseStream(), Encoding.GetEncoding("utf-8")).ReadToEnd();
        Console.WriteLine(responseString.ToString());
        Console.ReadLine();

string jsonParam = "{appId:1122,CODE:3344}"; 改成json格式试试

    request.ContentType = "application/json"; 改成 request.ContentType = "application/json;charset=UTF-8"; 看看

500 是服务端拒绝响应，多半是服务端程序错误