Enviar y recibir SMS mensajes desde una aplicación C#

using System;
using System.IO;
using System.Net.Http;
using System.Net.Http.Headers;
using System.Threading.Tasks;
using System.Text;
using System.Web;
 
/**
* Function parameters:
*
* - accessToken (required)
* - message (required)
* - destinataires (required): Receivers separated by a comma
* - emetteur (optional): Allows to deal with the sms sender
* - optionStop (optional): Deal with the STOP sms when marketing send (cf. API HTTP documentation)
* - batchFilePath (required for batch mode): The path of CSV file for sms in Batch Mode
*/
 
namespace ExempleClientHttpApi
{
 public class ExempleClientHttpApi {
 
 private static string URL = "https://api.smsmode.com/http/1.6/";
 private static string PATH_SEND_SMS = "sendSMS.do";
 private static string PATH_SEND_SMS_BATCH = "sendSMSBatch.do";
 private static string ERROR_API = "Error during API call\n";
 private static string ERROR_FILE = "The specified file does not exist\n";
 private static readonly HttpClient _httpClient= new HttpClient();
 
 public ExempleClientHttpApi()
 {
 Encoding.RegisterProvider(CodePagesEncodingProvider.Instance);
 }
 
 // send SMS with GET method 
 public string sendSmsGet(string accessToken, string message, string destinataires, string emetteur, string optionStop) { 
 
 string urlEncodedMessage = HttpUtility.UrlEncode(message, Encoding.GetEncoding("ISO-8859-15"));
 string finalUrl = URL + PATH_SEND_SMS + "?accessToken=" + accessToken + "&numero=" + destinataires + "&message=" + urlEncodedMessage + "&emetteur=" + emetteur + "&stop=" + optionStop;
 
 return Get(finalUrl).Result;
 }
 
 public static async Task<string> Get(string url){
 
 try {
 var response = await _httpClient.GetAsync(url);
 string result = await response.Content.ReadAsStringAsync();
 return result;
 } catch (Exception) {
 return ERROR_API;
 }
 }
 
 // send SMS with POST method 
 public string sendSmsPost(string accessToken, string message, string destinataires, string emetteur, string optionStop) {
 
 string finalUrl = URL + PATH_SEND_SMS;
 
 StringBuilder sb = new StringBuilder();
 sb.Append("accessToken=" + accessToken);
 sb.Append("&numero=" + destinataires);
 sb.Append("&emetteur=" + emetteur);
 sb.Append("&message=" + HttpUtility.UrlEncode(message, Encoding.GetEncoding("ISO-8859-15")));
 sb.Append("&stop=" + optionStop);
 
 return Post(finalUrl ,Encoding.Default.GetBytes(sb.ToString())).Result;
 }
 
 public static async Task<string> Post(string url, byte[] data){
 
 ByteArrayContent byteContent = new ByteArrayContent(data);
 byteContent.Headers.ContentType = new MediaTypeHeaderValue("application/x-www-form-urlencoded");
 try {
 var response = await _httpClient.PostAsync(url, byteContent);
 string result = await response.Content.ReadAsStringAsync();
 return result;
 } catch (Exception) {
 return ERROR_API;
 }
 }
 
 // send SMS with POST method (batch)
 public string sendSmsBatch(string accessToken, string batchFilePath, string optionStop) {
 
 if (!File.Exists(batchFilePath)) {
 return ERROR_FILE;
 }
 string finalUrl = URL + PATH_SEND_SMS_BATCH + "?accessToken=" + accessToken + "&stop=" + optionStop;
 return PostBatch(finalUrl , File.ReadAllBytes(batchFilePath), batchFilePath).Result;
 }
 
 public static async Task<string> PostBatch(string url, byte[] data, string batchFilePath) {
 
 var requestContent = new MultipartFormDataContent();
 ByteArrayContent byteContent = new ByteArrayContent(data);
 byteContent.Headers.ContentType = MediaTypeHeaderValue.Parse("text/csv");
 requestContent.Add(byteContent, "file", batchFilePath);
 try {
 var response = await _httpClient.PostAsync(url, requestContent);
 string result = await response.Content.ReadAsStringAsync();
 return result;
 } catch (Exception) {
 return ERROR_API;
 }
 }
 }
}