Trade Inquiry: Steam <-> GOG ?

Hello, I am not sure if this is the right place to ask this question but, can I, as someone who got the game from GOG, trade items with someone with a Steam copy?

I ask this mostly because all of the trade threads seem to be Steam-only, and I really wanna trade some Epics I don’t need for some I want…

No reason for it not to work. The save files are created the same for both versions.

But GOG user cannot join internet play with Steam user right now, right?

This is Right. You can only exchange savefiles outside the game.

Hm, I see, so I would just have to share that ‘‘transfer.gst’’ file from the saves folder? Or is it some other one?