Binance.net object reference not set to instance of object.

API Futures API
1

I am trying to place future order at binance test but getting exception.
code:
var client = TestHelpers.CreateClient( new BinanceClientOptions("",Common.apiURL ,"")
{
ApiCredentials = new ApiCredentials(Common.apiKey,Common.apiSecret),
AutoTimestamp = false,
LogVerbosity= LogVerbosity.Debug ,
LogWriters= new List { (new StreamWriter(Path.Combine(Application.StartupPath, “logs.txt”)))}

        });
        
        // act
        var result = client.FuturesUsdt.Order.PlaceOrder("BTCUSDT", OrderSide.Buy, OrderType.Limit, timeInForce: TimeInForce.GoodTillCancel, quantity: 1, price: 2000);

Exeption:
System.NullReferenceException: ‘Object reference not set to an instance of an object.’

This exception was originally thrown at this call stack:
[External Code]
Binance.Net.SubClients.Futures.BinanceClientFuturesOrder.PlaceOrderAsync(string, Binance.Net.Enums.OrderSide, Binance.Net.Enums.OrderType, decimal?, Binance.Net.Enums.PositionSide?, Binance.Net.Enums.TimeInForce?, bool?, decimal?, string, decimal?, decimal?, decimal?, Binance.Net.Enums.WorkingType?, bool?, Binance.Net.Enums.OrderResponseType?, int?, System.Threading.CancellationToken) in BinanceClientFuturesOrder.cs

APIBaseURL: https://testnet.binancefuture.com