How to consume rest api in C#

I want to consume rest api having post method in my project (web)/Windows service(C#).

Url :

I need to pass username and password for generating token. I have written code like this.

string sURL = "";
WebRequest wrGETURL;
wrGETURL = WebRequest.Create(sURL);

wrGETURL.Method = "POST";
wrGETURL.ContentType = @"application/json; charset=utf-8";
wrGETURL.ContentLength = 0;
HttpWebResponse webresponse = wrGETURL.GetResponse() as HttpWebResponse;

Encoding enc = System.Text.Encoding.GetEncoding("utf-8");
// read response stream from response object
StreamReader loResponseStream = new StreamReader(webresponse.GetResponseStream(), enc);
// read string from stream data
string strResult = loResponseStream.ReadToEnd();
// close the stream object
// close the response object


I am getting error: No connection could be made because the target machine actively refused it

Is it right way to consume rest api in C#?