I had similar issues finding matching items and  not receiving the check mark even when I did.  It seems to happen when there are duplicate items required in the cauldron.  It's a really nice-looking game and the mechanics work well for the most part.  I would like to be able to trade my items with the chest without having to throw them out, since I'm always scrambling to cycle items as quickly as possible.  More inventory slots would help this too, I suppose.

Edit: my hypothesis about the duplicate items was incorrect, it just happens randomly.  I want to see the ending but I keep either not being able to find all the items or it doesn't accept them!

Can't find the required items even though I searched and tried trading everywhere!

Ran into a crash at the end, as I couldn't find the required cups and guess the fireball wasn't sure where to go? Really sweet artwork and nice music in this game, but the gameplay was kind of basic.

Certainly pretty but really not much of a game! Seems like a novel concept and some fantastic art style direction if you decide to keep going with this one!