Program.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Net.WebSockets;
using System.Text;
using System.Threading;
using System.Threading.Tasks;
using Newtonsoft.Json.Linq; // install Json.NET from 'Manage Nuget Packages...' menu

namespace blinktrade_websocket_client
{
    class Program
    {
        private static async Task BlinkTradeWebSocketTest()
        {
            using (ClientWebSocket ws = new ClientWebSocket())
            {
                // connect to blinktrade gateway
                Console.WriteLine("Waiting connection...");
                Uri serverUri = new Uri("wss://api.testnet.blinktrade.com/trade/");
                await ws.ConnectAsync(serverUri, CancellationToken.None);

                // Build the json Login Request Message
                int reqid = 1;
                JObject json_login_request = new JObject();
                json_login_request["MsgType"] = "BE";
                json_login_request["UserReqID"] = reqid;
                json_login_request["Username"] = "user";
                json_login_request["Password"] = "abc12345";
                json_login_request["UserReqTyp"] = "1";
                json_login_request["BrokerID"] = 5;
                json_login_request["UserAgent"] = "Mozilla/5.0 (Linux; Android 6.0; Nexus 5 Build/MRA58N) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/46.0.2490.76 Mobile Safari/537.36";
                json_login_request["UserAgentLanguage"] = "en-US";
                json_login_request["UserAgentTimezoneOffset"] = ":180,";
                json_login_request["UserAgentPlatform"] = "Linux x86_64";
                json_login_request["FingerPrint"] = "264206477";
                JObject json_stuntip = new JObject();
                json_stuntip["local"] = "192.168.0.12;";
                json_stuntip["public"] = new JArray("177.35.172.183");
                json_login_request["STUNTIP"] = json_stuntip;

                // Send Login Request Message on wire AS String
                string login_request_message = json_login_request.ToString();
                ArraySegment<byte> bytesToSend = new ArraySegment<byte>(Encoding.UTF8.GetBytes(login_request_message));
                
                Console.WriteLine("Sending login request...");
                Console.WriteLine("[-->]: " + login_request_message);
                
                await ws.SendAsync( 
                    bytesToSend,  
                    WebSocketMessageType.Text,  
                    true, 
                    CancellationToken.None);

                while (ws.State == WebSocketState.Open)
                {
                    // Receive the response
                    ArraySegment<byte> bytesReceived = new ArraySegment<byte>(new byte[4096]);
                    WebSocketReceiveResult result = await ws.ReceiveAsync(bytesReceived, CancellationToken.None);
                    Console.WriteLine("[<--]: " + Encoding.UTF8.GetString(bytesReceived.Array, 0, result.Count));
                    
                    // build the Test Request using string manipulation instead of a Json Library
                    string test_request_msg = "{\"MsgType\":\"1\", \"TestReqID\":" + reqid.ToString() +"}";
                    Console.WriteLine("[-->]: " + test_request_msg);
                    
                    // Send Test Request 
                    bytesToSend = new ArraySegment<byte>(Encoding.UTF8.GetBytes(test_request_msg));
                    await ws.SendAsync( bytesToSend, WebSocketMessageType.Text, true, CancellationToken.None);
                    
                    // Increment the request id 
                    ++reqid;
                }
            }
        }
        
        static void Main(string[] args)
        {
            Task t = BlinkTradeWebSocketTest();
            t.Wait();
        }
    }
}