How to Send SMS using HTTP API in C# Code?

//Your user name
string user = "UR_USER";
//Your authentication key
string key = "UR_KEY";
//Multiple mobiles numbers separated by comma
string mobile = "9974984500";
//Sender ID,While using route4 sender id should be 6 characters long.
string senderid = "SENDER";
//Your message to send, Add URL encoding here.
string message = HttpUtility.UrlEncode("Test message");

//Prepare you post parameters

String sbPostData = "user={userid}&key={unique_id}&mobile={mobile_no}&message=test sms&senderid={senderid}&accusage={account_usage_type_id}";

   //Call Send SMS API
   string sendSMSUri = "";
   //Create HTTPWebrequest
   HttpWebRequest httpWReq = (HttpWebRequest)WebRequest.Create(sendSMSUri);
   //Prepare and Add URL Encoded data
   UTF8Encoding encoding = new UTF8Encoding();
   byte[] data = encoding.GetBytes(sbPostData.ToString());
   //Specify post method
   httpWReq.Method = "POST";
   httpWReq.ContentType = "application/x-www-form-urlencoded";
   httpWReq.ContentLength = data.Length;
   using (Stream stream = httpWReq.GetRequestStream())
   	stream.Write(data, 0, data.Length);
   //Get the response
   HttpWebResponse response = (HttpWebResponse)httpWReq.GetResponse();
   StreamReader reader = new StreamReader(response.GetResponseStream());
   string responseString = reader.ReadToEnd();
   //Close the response
catch (SystemException ex)