Error: Server returned a fault exception: [1] [InvalidConfig]

I have installed from nugets the InfusionSoft library - Eventday and also the XML-RPC client library. Below are the codes.

const string application = “”;
//AccessToken is what I used to call for REST API and it is working.
var customer = new Customer(application, _cred.AccessToken);
var client = customer.Connect();
System.Net.ServicePointManager.SecurityProtocol = System.Net.SecurityProtocolType.Tls12;
var cs = client.DataService.FindByField(
table: “Order”,
limit: 5,
page: 0,
fieldName: “Id”,
fieldValue: id.ToString(),
returnFields: new { “_SalespersonCode”, “_OrderWarehouse”, “_TerritoryField”, “_ExpectedDeliveryDate”, “_ExporttoPronto” });

This is the detailed error: {“Server returned a fault exception: [1] [InvalidConfig]For API support, please go to If you need to submit an API trouble ticket, go to”}

Can someone help me why I am having this error? I have tried many times testing and everytime it come up with same error.

Thank you