كيف اتعامل مع هذا API

السلام عليكم

محتاج الساعده ضرورى جدا فى الموضوع ده يا جماعه

انا معى API sms

محتاج اتعامل معاه

ازى ابعت المتغيرات واستقبل الرد منه باى طريقه

انا هنا مستعمل and httpwebrequest httpwebresponse

الرابط الخاص ب API

http://www.resalty.net/api/sendSMS.php?userid=YouUser&password=YourPassword&to=MobileNumber&msg=Message&sender=SenderName

string url = "http://www.resalty.net/api/sendSMS.php?";

        StringBuilder postData = new StringBuilder();

        postData.Append("userid=" + HttpUtility.UrlEncode("user") + "&");
        postData.Append("password=" + HttpUtility.UrlEncode("pass") + "&");
        postData.Append("to=" + HttpUtility.UrlEncode(to) + "&");
        postData.Append("msg=" + HttpUtility.UrlEncode(Msg) + "&");
        postData.Append("sender=" + HttpUtility.UrlEncode("sendernum") );
HttpWebRequest request = (HttpWebRequest)WebRequest.Create(url);
        request.Method = "POST";
        request.ContentType = "application/x-www-form-urlencoded";
        request.ContentLength = postData.ToString().Length;

        try
        {
            writer = new StreamWriter(request.GetRequestStream());
            writer.Write(postData.ToString());

            HttpWebResponse response = (HttpWebResponse)request.GetResponse();

            Stream receiveStream = response.GetResponseStream();

            StreamReader readStream = new StreamReader(receiveStream, Encoding.UTF8);


            Label3.Text = readStream.ReadToEnd();

        }