Can not get json data when call API

In index.asp page when click a button, the post will call
void post (string api, string json, string token)
        {
            DefaultController DC = new DefaultController();
            DC.Insertdb(json);

            string url = api + "/Default/Insertdb?json=" + json;

            //string postData = "json=" + json;
            //ASCIIEncoding encoding = new ASCIIEncoding();
            //byte[] byte1 = encoding.GetBytes(postData);

            System.Net.WebRequest req = WebRequest.Create(url);
            req.Method = "POST";
            req.Timeout = 30000;
            req.ContentType = "application/json;charset=UTF-8";
            req.ContentLength = 0;

            WebResponse response = req.GetResponse();

Here is Insertdb:
public dynamic Insertdb(string json)
        {
            Results _result = new Results();

            var jsonData = JsonConvert.DeserializeXmlNode(json);
            dynamic jsonData1 = JsonConvert.DeserializeXmlNode(json);
            string xmlData = jsonData.OuterXml;
            xmlData = "<NewDataSet>" + xmlData + "</NewDataSet>";

            DBHelp db = new DBHelp();

            db.AddParameter("@_DataConvert", xmlData);

            try
            {
                SqlDataReader reader = db.ExecuteReader("usp_SyncData_Bravo_CRM_Add", CommandType.StoredProcedure);

When i trace by fiddler, it not have JSON result