Hi steve, just to notice that i had the exact same problem as Sanghoon (trial expired, special NaNoWriMo) i first thought there is a wrong link on your website that direct to the wrong trial file from the mac page : https://storyist.com/mac/
But the link you gave https://update.storyist.com/downloads/Storyist.dmg also direct to a version saying that "This special NaNoWriMo trial version expired on December 15, 2019?
For now i found a way to not have this problem by downloading the App Store version but i fear you may lost some customers here
Sincerely
Yann