I've found a bug I think: When I bought a new Level of Rod with the exact amount of gems needed my Gems were set to -1 therefore erroneously increasing the amount of gems I need to obtain for each level by one
Oh my, that's an embarrassing mistake! I'll fix that asap, but you'll have to re-download the game when I've made the fix. Thank you for reporting it!
I've fixed the issue 🙏
