How to erase all notes?
NotePlan saves all your notes on your local devices and syncs them using Apple's CloudKit or iCloud Drive. Depending on your sync methods, there are different ways to delete everything local and in the cloud.
Use the advanced sync preferences inside NotePlan on Mac and iOS. If "CloudKit" is selected in the preferences, click on the "Advanced" option, then "Delete Local and Cloud Database":
You have to do this on every device once.
If you are using iCloud Drive, you can open NotePlan's iCloud Drive folder and delete it: