The digital art world is not happy with Clip Studio Paint.
Up until now (well, until 2023) a one time purchase gave you the program and regular updates. This was the case for a decade, but as of the upcoming version 2.0 you’ll have to pay monthly for updates, even if you buy the “perpetual license.”
It sounds like letting your license laps also reverts you to the last perpetual license version you bought.
I covered this in a couple YouTube videos below.