Looks like the code is seeing your
urlParameters as a relative URL and appending the slash to the base URL as it is designed to.
HttpClient.BaseAddress Property (System.Net.Http) | Microsoft Docs[
^]
Remarks:
When sending a HttpRequestMessage with a relative Uri, the message Uri will be added to the BaseAddress property to create an absolute Uri.
What I would do to get around this is to
not set the BaseAddress at all and pass the URL directly into the GetAsynch method
string urlParameters = "?children=true";
HttpClient client = new HttpClient();
client.DefaultRequestHeaders.Accept.Add(new mediaTypeWithQualityHeaderValue("application/json"));
HttpResponseMessage response = client.GetAsync("https://app.smartfile.com/api/2/path/info" + urlParameters).Result;