How to call/Consume post API with Header in C#

This is simple sample code written to consume post API which has header  

Here I am using newtonsoft dll to convert class into json

    //using Newtonsoft.Json

    private void PostWithHeader()

    {

        WebRequest req = null;

        WebResponse rsp = null;

        string url = "http://"; // Pass url here

        string API_Response = "";

        jsonParameter P = new jsonParameter() { userid=1};

        try

        {

            req = WebRequest.Create(url);

            //Uncomment below line if Post with Basic auth also pass username & passord

            // req.Headers.Add(HttpRequestHeader.Authorization "Basic " + Convert.ToBase64String(System.Text.ASCIIEncoding.ASCII.GetBytes("userName:password")));

            //Uncomment below line If you want pass header key & their value also change key name & value           

            //req.Headers.Add("accesskey", "ccc"); //Key & Value

            req.Method = "post";

            req.ContentType = "application/json; charset=UTF-8";// "application/json"; //x-www-form-urlencoded";

            StreamWriter writer = new StreamWriter(req.GetRequestStream());

            writer.Write(JsonConvert.SerializeObject(P)); // Pass parameter as class

            writer.Close();

            // Send the data to the webserver

            rsp = req.GetResponse();

            StreamReader reader = new StreamReader(rsp.GetResponseStream());

            API_Response = reader.ReadToEnd();

            //return JsonConvert.DeserializeObject(API_Response);

            //return API_Response;

            Response.Write(API_Response);

        }

        catch (Exception ex)

        {

        }

    }

    public class jsonParameter

    {

        public int userid { get; set; }

    }