Send OTP ( One Time Password ) SMS to Verify user Mobile Number in Asp.Net C#

Important Namespaces Used
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using System.Net;
using System.Data;
using System.Data.SqlClient;
using System.Collections.Specialized;


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(Send Otp) Button Click Event Coding
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Panel1.Visible = false;
        Panel2.Visible = true;
        Random random = new Random();
        int value = random.Next(1001, 9999);
        string destinationaddr = "91" + TextBox1.Text;
        string message = "Your OTP Number is " + value + " ( Sent By : Coding Logic and Syntax )";
        //Label3.Text = message;
        String message1 = HttpUtility.UrlEncode(message);

        using (var wb = new WebClient())
        {
            byte[] response = wb.UploadValues("https://api.textlocal.in/send/", new NameValueCollection()
                {
                {"apikey" , "FammnpFW0Ks-gRKkiQvnke2nG940NkDbbl4jUV4elK"},
                {"numbers" , destinationaddr},
                {"message" , message1},
                {"sender" , "TXTLCL"}
                });
            string result = System.Text.Encoding.UTF8.GetString(response);
            Session["otp"] = value;


        }


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( Verify ) Button Click Event Coding
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 if(TextBox2.Text==Session["otp"].ToString())
        {
            Panel2.Visible = false;
            Label3.Text = "Your Mobile Number Has Been Verified Successfully - Thanks";
        }
        else
        {
            Label3.Text = "OTP Number is Not Correct : Your Mobile Number not Verified";
            Panel2.Visible = true;
        }


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