Thanks for playing!
In case you're curious, the invest button was originally supposed to add all of your damage to your money, but PICO-8 has some issues with changing big numbers easily or quickly. (Everything is a signed 16-bit integer, meaning that the highest number you can store without some math magic is around 32000. This is why the upgrades don't get more expensive past 30k.) So I decided to change the mechanic to delete any remaining money before adding, which I hoped would add a little bit of strategy while also fixing stuff behind the scenes... I do kind of regret not making it more intuitive though.