Why getting error Unable to connect to the remote server while executing HttpWebRequest.

HttpWebRequest request = (HttpWebRequest)WebRequest.Create(APIURL);

string strData = null;
            
            strData = "-------- data to assign---------";
            ASCIIEncoding encoding = new ASCIIEncoding();
            byte[] data = encoding.GetBytes(strData);

            request.Method = "POST";
            request.ContentType = "application/x-www-form-urlencoded";
            request.Accept = "text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8";
            request.KeepAlive = true;
            request.UserAgent = "Custom Agent";
            request.ContentLength = data.Length;
            request.AllowAutoRedirect = true;
            request.Timeout = (int)new TimeSpan(0, 0, 60).TotalMilliseconds;
            request.ServicePoint.Expect100Continue = false;

	    Stream newStream = request.GetRequestStream();

I getting above error at following line

Stream newStream = request.GetRequestStream();