Whenever you hit the cast button on cantrips in the character creator, a pop-up appears that says that you can't use it because you've used up all of your spell slots and there's no way to stop it because there's no space for level 0 spell slots. The app makers need to either fix this problem in a future update or just remove the cast button on cantrips since they can be cast at will without using spell slots and therefore don't need a cast button.