I can't recall. I think I was around wave 16 or something? It cost around 279 coins to upgrade if I remember, and I had over 300 at the time, but couldn't upgrade fire rate further.
Always happy to give feedback. Plus, Stoff's my boy. Great lil jam game.
Oh, that's on me! We last-minute put in the UI interface and I didn't get to properly remove the button at some point. Basically, you have reached the cap on fire rate hence it wasn't available anymore, it's meant to have some user feedback at this point :D
