public string SendSMS(string _message, string _phone_number)
    {
        var enc = System.Text.Encoding.GetEncoding("EUC-JP");
        var postData = "";

        try
        {
            //POST送信する文字列を作成
            postData = postData + String.Format("username={0}&", HttpUtility.UrlEncode(_username));
            postData = postData + String.Format("password={0}&", HttpUtility.UrlEncode(_password));
            postData = postData + String.Format("trigger_id={0}&", HttpUtility.UrlEncode(_trigger_id1));
            postData = postData + String.Format("phone_number={0}&", HttpUtility.UrlEncode(_PhoneNumber));
            postData = postData + String.Format("message={0}&", HttpUtility.UrlEncode(_message));

            //バイト型配列に交換
            var postDataBytes = System.Text.Encoding.ASCII.GetBytes(postData);
            //WebRequestの作成
            System.Net.WebRequest req = System.Net.WebRequest.Create(_SMSURL);

            req.Timeout = System.Threading.Timeout.Infinite;

            //メソッドにPOSTを指定
            req.Method = "POST";
            //ContentTypeを"application/x-www-form-urlencoded"にする
            req.ContentType = "application/x-www-form-urlencoded";
            //POST送信するデータの長さを指定
            req.ContentLength = postDataBytes.Length;
            //データをPOST送信するためのStreamを取得
            System.IO.Stream reqStream = req.GetRequestStream();

            //送信するデータを書き込む
            reqStream.Write(postDataBytes, 0, postDataBytes.Length);

            reqStream.Close();

            //サーバーからの応答を受信するためのWebResponseを取得
            var res = req.GetResponse();
            //応答データを受信するためのStreamを取得
            var resStream = res.GetResponseStream();
            //XML形式へ
            var objXMLReader = new XmlTextReader(resStream);

            var xmldoc = new XmlDocument();
            xmldoc.Load(objXMLReader);
            objXMLReader.Close();


        }
        catch(Exception e)
        {
            return " Send SMS Error " + e.Message + " log:" + _log;
        }
    }

ServicePointManager.SecurityProtocol |= SecurityProtocolType.Tls11 | SecurityProtocolType.Tls12;