c# binance api открытие ордера

Уже второй день ломаю голову, где-то замылился взгляд. Пытаюсь открыть тестовый ордер на binance. Вот код:

    internal class Credentials
    {
        [JsonProperty("symbol")]
        public string Symbol { get; set; }
        [JsonProperty("side")]
        public string Side { get; set; }
        [JsonProperty("type")]
        public string Type { get; set; }
        [JsonProperty("timeInForce")]
        public string TimeInForce { get; set; }
        [JsonProperty("quantity")]
        public decimal Quantity { get; set; }
        [JsonProperty("price")]
        public decimal Price { get; set; }
        [JsonProperty("recvWindow")]
        public int RecvWindow { get; set; }
        [JsonProperty("timestamp")]
        public string Timestamp { get; set; }
       
        
        
    }
    //открытие позиции
    public async void CreateOrder(string instrument_name, string side, string type, double price, double quantity)
    {

        string path = "/api/v3/order/test?";
        string timeInForce = "GTC";
        int recvWindow = 5000;
        string time = GetTimestamp();
        string sign = GetSign_binance("symbol=" + instrument_name + "&side=" + side + "&type=" + type + "&timeInForce=" + timeInForce + "&quantity=" + Convert.ToDecimal(quantity) + "&price=" + Convert.ToDecimal(price) + "&recvWindow=" + recvWindow + "&timestamp=" + time);
        string url = API_URL_binance + path + "symbol=" + instrument_name + "&side=" + side + "&type=" + type + "&timeInForce=" + timeInForce + "&quantity=" + Convert.ToDecimal(quantity).ToString().Replace(",", ".") + "&price=" + Convert.ToDecimal(price).ToString().Replace(",", ".") + "&recvWindow=" + recvWindow + "&timestamp=" + time + "&signature=" + sign;
        string r;

        var Payload = new Credentials
        {
            Symbol = instrument_name,
            Side = side,
            Type = type,
            Quantity = Convert.ToDecimal(quantity),
            Price = Convert.ToDecimal(price),
            TimeInForce = timeInForce,
            RecvWindow = recvWindow,
            Timestamp = time
        };
        
        var stringPayload = JsonConvert.SerializeObject(Payload);


        HttpContent httpContent = new StringContent(stringPayload, Encoding.UTF8, "application/x-www-form-urlencoded");
        top.Invoke((ThreadStart)delegate ()
        {
            top.AppendText(DateTime.Now + " " + stringPayload + "\r\n");
        });

        System.Diagnostics.Stopwatch sw = new Stopwatch();
        using (var response = await client_binance.PostAsync(url, httpContent).ConfigureAwait(false))
            r = await response.Content.ReadAsStringAsync().ConfigureAwait(false);
        sw.Stop();

        top.Invoke((ThreadStart)delegate ()
        {
            top.AppendText(DateTime.Now + " " + r + "\r\n");
            top.AppendText(DateTime.Now + " " + url + " Время запроса: " + sw.ElapsedMilliseconds + "\r\n");
        });
    }

На выходе получаю ошибку:

{
    "code":-1104,
    "msg":"Not all sent parameters were read; read '9' parameter(s) but was sent '10'."
}

Соответственно отправляемый json

{
    "symbol":"BUSDUSDT",
    "side":"BUY",
    "type":"LIMIT",
    "timeInForce":"GTC",
    "quantity":10.1,
    "price":0.9994,
    "recvWindow":5000,
    "timestamp":"1639325197716"
}

И ссылка куда отправляю:

api3.binance.com/api/v3/order/test?symbol=BUSDUSDT&side=BUY&type=LIMIT&timeInForce=GTC&quantity=10.1&price=0.9994&recvWindow=5000&timestamp=1639325197716&signature=307dc0dce20835f3a80e40f11406d446d9f20e5edfdf5300229ddd026bef6b8c

Что я делаю не так?