Free Game Engine for Real Time Collaboration

Hi!

I'm looking for a recommendation on a game engine that I can use to work with a friend in real time. I've tried Unity already and can't seem to get Unity Teams to work with my friend. If it matters, we're looking to make a digital card game (similar to Hearthstone, Shadowverse, or Legends of Runeterra). Any help would be useful!

Thanks in advance.