.NET assembly dependencies

I wrote a small .NET assembly to dispatch some notifications, but that assembly uses a few things:

    using System.Net;
    using System.Net.Http;
    using System.Runtime.Serialization.Json;

Is that okay?  Those are all things that come with the PlantSCADA 2023 version of .NET (which is version 4.8).

The first thing I wrote to test was this:

public string test()
{
    return "hello";
}

That worked great.  The second thing I did formed a JSON message and sent it as an HTTP POST.  That didn't work - from the CiCode side, the function call returns, but it doesn't return any content.  My thinking here is it's a dependency management problem.

Cicode side: 

STRING dllPath = "C:\work\aveva\Squadcast\bin\Debug\net48\Squadcast.dll"
STRING msg;
STRING result;

squadcastClient= DllClassCreate(dllPath, "SquadcastClient")

IF DllClassIsValid(squadcastClient) <> 1 THEN
   msg = IntToStr(squadcastClient);
   Message("Error", msg, 0);
ELSE
   result = DllClassCallMethod(squadcastClient, "test");
   Message("result", "returned " + result, 0);
   DllClassDispose(squadcastClient);
END;