I loved how quickly the app started up and immediately had me at an interactive step.
I think you really need to have 10-20 levels, not 2, before interrupting with the CTA for paying. I had only just learned the basic rules and had no clue if I liked the game or what hints would even be worth to me.
I was going to comment that the frame rate and responsiveness was oddly bad but when I went back to check a few things it was buttery smooth. Dunno if that was just a weird one-off or something that happens on first launch?
Let me hide the timer. I know, it’s silly. But it truly affects my enjoyment of nonogram games.
I like the simple little beeps it makes when toggling. Have you considered picking triads from different keys? This can break the monotony. You could pick a random key each game and different chords from that key!
Overall this is well done. You should feel proud of your accomplishment!