I have had the same problem. I have looked several times to find a game and it says "number of online players- 0". And I think you can't put up an invitation for someone to accept later. You have to stay online, right, until someone accepts it?
If you add friends inside the app, you can send invites to them without the need to wait for them to joing the game. After the 1.1 update, they will also receive a push notification about your invite! Note that to add a person as "friend", you just need to know their username.
Thanks for your feedback, anyway! Both Studio Clangore (the app developers) and Asmodee Digital (the app distributor) are working to improve both the app and the online infrastructure.
I was hoping the issue would be fixed after the last update. Either nobody is playing the game online or something is still broken. I can't believe most of the time when I'm on it only shows only 1-2 people online.