how to integrate SMS feature in asp.net web application?

using System;
using System.Web;
using System.Web.UI;
using System.Threading.Tasks;
using RingCentral;
using System.Web.UI.WebControls;
namespace RingCentral_SMS
{
    public partial class Default : System.Web.UI.Page
    {
        RestClient rc = null;
        const string RINGCENTRAL_CLIENTID = "Your_App_Client_Id";
        const string RINGCENTRAL_CLIENTSECRET = "Your_App_Client_Secret";         const string RINGCENTRAL_USERNAME = "Your_Username";         const string RINGCENTRAL_PASSWORD = "Your_Password";         const string RINGCENTRAL_EXTENSION = "ExtensionNumber";         protected void sendMessageButton_Clicked(object sender, EventArgs e)         {             LoginRingCentralAsync().Wait();         }         private async Task LoginRingCentralAsync()         {             if (rc == null)             {                 rc = new RestClient(RINGCENTRAL_CLIENTID, RINGCENTRAL_CLIENTSECRET, false);                 await rc.Authorize(RINGCENTRAL_USERNAME, RINGCENTRAL_EXTENSION, RINGCENTRAL_PASSWORD);                 if (rc.token.access_token.Length > 0)                 {                     result.InnerHtml = "Authorized";                     SendMessageAsync().Wait();                 }                 else                 {                     result.InnerHtml = "Unauthorized";                 }             }         }         private async Task SendMessageAsync()         {             var parameters = new CreateSMSMessage();             parameters.from = new MessageStoreCallerInfoRequest { phoneNumber = sendFrom.Value };             parameters.to = new MessageStoreCallerInfoRequest[] { new MessageStoreCallerInfoRequest { phoneNumber = sendTo.Value } };             parameters.text = subject.Value;             var resp = await rc.Restapi().Account().Extension().Sms().Post(parameters);             result.InnerHtml = resp.messageStatus;         }     } }

<%@ Page Language="C#" Inherits="RingCentral_SMS.Default" %>
<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <title>RingCentral Connect Platform Demo</title>
</head>
<body>
    <h2>RingCentral APIs Demo</h2>
    <form id="form2" method="post" enctype="multipart/form-data" runat="server">
        <div>
            <h3>Messaging Demo</h3>
            <span>From</span>
            <input type="text" id="sendFrom" name="text" size="20" runat="server"/> <br/>
            <span>To</span>
            <input type="text" id="sendTo" name="text" size="20" runat="server"/> <br/>
            <span>Text message</span>
            <input type="text" id="subject" name="text" size="100" runat="server"/> <br/>
            <asp:Button ID="Button2" Text="Send" runat="server" onClick="sendMessageButton_Clicked"/>
        </div>
    </form>
    <br/>
    <div>Result:</div>
    <div id="result" runat="server" />
</body>
</html>