C# API call Bitstamp, still not working..

using RestSharp;
using System;
using System.Security.Cryptography;
using System.Text;

namespace ConsoleApp5
{
    class Program
    {
        private readonly String _clientId = "xxx";
        private readonly String _apiKey = "xxx";
        private readonly String _apiSecret = "xxx";

        static void Main()
        {
            Program program = new Program();

            RestRequest request = new RestRequest("/api/v2/balance/", Method.POST);

            program.AddApiAuthentication(request);

            Console.ReadLine();
        }

        public void AddApiAuthentication(RestRequest restRequest)
        {
            var nonce = DateTime.Now.Ticks;
            var signature = GetSignature(nonce, _apiKey, _apiSecret, _clientId);
            long time = DateTime.UtcNow.Ticks / TimeSpan.TicksPerMillisecond;
            string version = "v2";
            string contentType = "application/x-www-form-urlencoded";

            restRequest.AddParameter("X-Auth", _apiKey);
            restRequest.AddParameter("X-Auth-Signature", signature);
            restRequest.AddParameter("X-Auth-Nonce", nonce);
            restRequest.AddParameter("X-Auth-Timestamp", time);
            restRequest.AddParameter("X-Auth-Version", version);
            restRequest.AddParameter("Content-Type", contentType);


            RestClient client = new RestClient
            {
                BaseUrl = new Uri("https://www.bitstamp.net/")
            };

            IRestResponse response = client.Execute(restRequest);
            Console.WriteLine(response.Content);
        }

        private string GetSignature(long nonce, string key, string secret, string clientId)
        {
            string msg = string.Format("{0}{1}{2}", nonce,
                clientId,
                key);

            return ByteArrayToString(SignHMACSHA256(secret, StringToByteArray(msg))).ToUpper();
        }
        public static byte[] SignHMACSHA256(String key, byte[] data)
        {
            HMACSHA256 hashMaker = new HMACSHA256(Encoding.ASCII.GetBytes(key));
            return hashMaker.ComputeHash(data);
        }

        public static byte[] StringToByteArray(string str)
        {
            return System.Text.Encoding.ASCII.GetBytes(str);
        }

        public static string ByteArrayToString(byte[] hash)
        {
            return BitConverter.ToString(hash).Replace("-", "").ToLower();
        }
    }
}