SMS Gateway

using Newtonsoft.Json;
using Newtonsoft.Json.Linq;
using System;
using System.IO;
using System.Net;
using System.Text;

namespace Lox24.Api
{
    class client
    {
        static void Main()
        {
            string key = "1234567:e3f3a759b6677959b6ebfcxxxxxxxxxx";
            string url = "https://api.lox24.eu/sms";

            var data = new {
                sender_id = "My Sender",
                text = "Test message",
                service_code = "direct",
                phone = "+49751234567",
                delivery_at = 1573724611,
                is_unicode = true,
                callback_data = "123456",
                voice_lang = "DE"
            };

            string postdata = JsonConvert.SerializeObject(data);

            Console.WriteLine("Post data: {0}", postdata);

            var httpWebRequest = (HttpWebRequest)WebRequest.Create(url);
            httpWebRequest.ReadWriteTimeout = 100000;
            httpWebRequest.ContentType = "application/json; charset=utf-8";
            httpWebRequest.Accept = "application/json"; // or application/ld+json
            httpWebRequest.Method = "POST";
            httpWebRequest.KeepAlive = true;
            httpWebRequest.Headers.Add("X-LOX24-AUTH-TOKEN", key);
            httpWebRequest.Credentials = CredentialCache.DefaultNetworkCredentials;

            using (var streamWriter = new StreamWriter(httpWebRequest.GetRequestStream()))
            {
                streamWriter.Write(postdata);
                streamWriter.Flush();
                streamWriter.Close();
            }
            try
            {
                using (HttpWebResponse resp = (HttpWebResponse)httpWebRequest.GetResponse())
                {

                    if(resp.StatusCode == HttpStatusCode.Created) {
                        Console.WriteLine("Success:{0} {1}", (int)resp.StatusCode, "sms resource created");
                    } else {
                        Console.WriteLine("Error: wrong response code {0} on create sms", (int)resp.StatusCode);
                    }

                    Stream respStream = resp.GetResponseStream();
                    using (StreamReader sr = new StreamReader(respStream, Encoding.UTF8))
                    {
                        string responseText = sr.ReadToEnd();
                        Console.WriteLine("responseText : {0}", responseText);
                    }
                }

            }
            catch (System.Net.WebException ex)
            {
                var webResponse = ex.Response as System.Net.HttpWebResponse;
                Console.WriteLine("Error:{0}", webResponse.StatusCode);

                switch (webResponse.StatusCode)
                {
                    case HttpStatusCode.BadRequest: // 400
                        Console.WriteLine("Error:400 Invalid input");
                        break;
                    case HttpStatusCode.Unauthorized: // 401
                        Console.WriteLine("Error:401 Client ID or API key isn't active or invalid!");
                        break;
                    case HttpStatusCode.PaymentRequired: // 402
                        Console.WriteLine("Error:402 There are not enough funds on your account!");
                        break;
                    case HttpStatusCode.Forbidden: // 403
                        Console.WriteLine("Error:403 Account isn't activated. Please wait or contact to support!");
                        break;
                    case HttpStatusCode.NotFound: // 404
                        Console.WriteLine("Error:404 Resource not found");
                        break;
                    case HttpStatusCode.InternalServerError: // 500
                    case HttpStatusCode.BadGateway: //502
                    case HttpStatusCode.ServiceUnavailable: // 503
                    case HttpStatusCode.GatewayTimeout: // 504
                        Console.WriteLine("System error! Please contact to LOX24 support!");
                        break;
                }
            }
        }
    }