Webservice working on localhost but not working on Plesk's Domain

Asalam Alaikum(Greetings)!

I created webservice and test it on different angles, but when i published it on hosting site of my Plesk's Domain, it is not working any more. In this webservice is use RestSharp and Newtonsoft.JSON. And after that the code is:

public string Order_Place(string Token, string MarketID, string SystemID, string SelectionID, string Side, string Size, string Price, string CustomerOrderRef)
{
        var client = new RestClient(BaseClass.API_url.ToString() + "/OrdersPlace");
        var request = new RestRequest(Method.POST);
        request.AddHeader("postman-token", "dab9cc78-3668-1995-ba2e-35e73edfb924");
        request.AddHeader("cache-control", "no-cache");
        request.AddHeader("content-type", "application/json");
        request.AddHeader("systemid", SystemID.ToString());
        request.AddHeader("marketid", MarketID.ToString());
        request.AddHeader("token", Token.ToString());
        PlaceOrderd bp = new PlaceOrderd
        {
            orderType = "LIMIT",
            handicap = 0,
            selectionId = Convert.ToInt32(SelectionID.ToString()),
            side = Side.ToString(),
            customerOrderRef = CustomerOrderRef.ToString(),
            limitOrder = new Limitorder
            {
                size = Convert.ToDecimal(Size.ToString()),
                price = Convert.ToDecimal(Price.ToString())
            }
        };
        List<PlaceOrderd> bplist = new List<PlaceOrderd>();
        bplist.Add(bp);

        request.AddParameter("application/json", Newtonsoft.Json.JsonConvert.SerializeObject(bplist), ParameterType.RequestBody);
        IRestResponse response = client.Execute(request);
        return response.Content.ToString();
}

It's working fine on localhost, but it's not working on domain.

public class PlaceOrderd
{
    public string orderType { get; set; }
    public int selectionId { get; set; }
    public float handicap { get; set; }
    public string side { get; set; }
    public Limitorder limitOrder { get; set; }
    public string customerOrderRef { get; set; }
}

public class Limitorder
{
    public decimal size { get; set; }
    public decimal price { get; set; }
}

The string return null only. Can any one help?

Thank you
Regards,

Muhamamad Naveed Haroon