yeah, we wanted a penalty for failing and a system that rewarded replay. So keys add up so if you grind the previous level you get that many tries at the next. And if you sell cards make money you can do more retrying. This was our first game ^^;
I think the problem with upgrading you are having is that one or more of the cards you are trying to combine are still in a deck. We weren’t able to get the game to not crash when you consumed a card that was in one of your decks. So you need to make sure they aren’t currently in one of the three presets. You can see what decks they are currently in when you click on them in the library. It is at the bottom of the info/pop up.