Message Send In C#

string authKey = authkey;
//Multiple mobiles numbers separated by comma
string mobileNumber = txtphno.Text;
//Sender ID,While using route4 sender id should be 6 characters long.
string senderId = username1;
//Your message to send, Add URL encoding here.
string msg = HttpUtility.UrlEncode(txtmessage.Text);
//Prepare you post parameters
StringBuilder sbPostData = new StringBuilder();
sbPostData.AppendFormat("authkey={0}", authKey);
sbPostData.AppendFormat("&mobiles={0}", mobileNumber);
sbPostData.AppendFormat("&message={0}", msg);
sbPostData.AppendFormat("&sender={0}", senderId);
sbPostData.AppendFormat("&route={0}", "4");
try {
    //Call Send SMS API
    string sendSMSUri = "Your key";
    //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
    reader.Close();
    response.Close();
    MessageBox.Show("Your Message has been Sent.", "Message"