How does a co-op work?

[Freya]

Hi forum
I have the game on Steam, my friend has it on Epic Game. How can we play together?
Online game settings - everything is open. Our lobbies are not found in the search for active sessions.
I see the Epic Games banner in the menu, but I log in to Epic Games through Google. Since the game does not have a Google banner, this makes linking impossible.
Please tell me how to solve the problem? Playing solo is very boring..