cTrader don't see reference to System.Windows; for .Net6.0

Hi all,

I'm having a strange problem and have run out of ideas on what else I can check. With the new .Net6.0 came the ability to easily use the MessageBox function.  I wanted to test it, in the code I added:

using System;
using System.Windows;
....
MessageBox.Show("Test message");

Unfortuntely during compilation/building it return exception:
"Error CS0103: The name 'MessageBox' does not exist in the current content ..." Strange as MessageBox is part of System.Windows. Even more strange when I open same indicator through Visual Studio 2022, compilation passes without errors

Any idea how to add references to be seen by cTrader properly and to compile propely using cTrader compiler ??