Send SMS with 💎 C#

// 1 — PRIMARY — use this
https://www.isms.com.my/isms_send_all_id.php
// 2 — Mirror — backup only
https://smtpapi2.vocotext.com/isms_send_all_id.php
// 3 — Mirror — backup only
https://smtpapi.vocotext.com/isms_send_all_id.php
// 4 — Mirror — backup only
https://ww3.isms.com.my/isms_send_all_id.php

using System;
using System.Collections.Generic;
using System.Net.Http;
using System.Threading.Tasks;

class IsmsSender
{
    // Reuse HttpClient — do not create per request
    private static readonly HttpClient _client = new HttpClient();

    static async Task<string> SendSmsAsync(string mobile, string message)
    {
        var payload = new Dictionary<string, string>
        {
            { "un",         "your_username"  },  // iSMS username
            { "pwd",        "your_password"  },  // iSMS password
            { "dstno",      mobile           },  // e.g. "601X-XXXXXXX"
            { "msg",        message          },
            { "type",       "1"              },  // 1 = ASCII, 2 = Unicode
            { "agreedterm", "YES"            },
            { "sendid",     "MyBrand"        }   // Optional, max 11 chars
        };

        var content  = new FormUrlEncodedContent(payload);
        var response = await _client.PostAsync(
            "https://www.isms.com.my/isms_send_all_id.php", content);

        var result = await response.Content.ReadAsStringAsync();
        return result;
    }

    static async Task Main()
    {
        var result = await SendSmsAsync("601X-XXXXXXX", "Hello from iSMS!");

        if (result.StartsWith("2000"))
        {
            var trxId = result.Split(':')[1];
            Console.WriteLine($"SMS sent! Transaction ID: {trxId}");
        }
        else
        {
            Console.WriteLine($"Failed: {result}");
        }
    }
}