var bitmexAuthorization = new BitmexAuthorization() 
{
  BitmexEnvironment = Bitmex.NET.Models.BitmexEnvironment.Test,
  Key = "your api key",
  Secret = "your api secret"
};
var bitmexApiService = BitmexApiService.CreateDefaultApi(bitmexAuthorization);

Container.RegisterType<IBitmexApiProxy, BitmexApiProxy>();
Container.RegisterType<IBitmexApiService, BitmexApiService>();

var authorization = new BitmexAuthorization
{
  BitmexEnvironment = Bitmex.NET.Models.BitmexEnvironment.Test,
  Key = "your api key",
  Secret = "your api secret"
};

Container.RegisterInstance<IBitmexAuthorization>(authorization);

private async void Sell()
{
  var posOrderParams = OrderPOSTRequestParams.CreateSimpleMarket("XBTUSD", Size, OrderSide.Sell);
  await _bitmexApiService.Execute(BitmexApiUrls.Order.PostOrder, posOrderParams).ContinueWith(ProcessPostOrderResult);
}

private class SomeQueryStringParams : QueryStringParams
{
  [DisplayName("val")]
  public string Value { get; set; }
}

private class SomeJsonParams : QueryJsonParams
{
  [JsonProperty("symbol")]
  public string Symbol { get; set; }
}

private class AResult
{
  [JsonProperty("value")]
  public string Value { get; set; }
}

var result = await bitmexApiService.Execute(new ApiActionAttributes<SomeJsonParams, AResult>("anApiMethod", HttpMethods.POST), new SomeJsonParams(){Symbol = "XBTUSD"});

// if the method returns an array of objects
var result = await bitmexApiService.Execute(new ApiActionAttributes<SomeJsonParams, List<AResult>>("anApiMethod", HttpMethods.POST), new SomeJsonParams(){Symbol = "XBTUSD"});