Can I play CE co-op though not all is downloaded?

When i try to join their game it says “please ensure all players in the party have the same version of the game” and doesn’t let me connect

For me, I know I have to have downloaded the campaign for the specific game I want to play, otherwise I get the message you mention. It’s the same for multiplayer, with the problem just being we can’t play the game if we don’t have all the assets and stuff downloaded.

Hope this answers your question!

It is also possible that one of you missed an update, there was one yesterday