My encrypted Joplin notes were syncing fine between my Windows laptop and my Android Phone until I decided to change my encryption password. I followed the instructions to change the encryption password, but something went wrong. I suspect sitting in Joplin on Android and Windows at the same time must have caused the encryption to stop working. At first it seemed to work, but once I edited a file on Windows it synced across to Android "encrypted" I was prompted to set my password, but i wasn't able to set the password. I deleted the Joplin Android App and reinstalled it, but I got the same result.
The Joplin Windows App has 3 Master Keys listed in the encryption section. Two of the Master keys have a source of "joplin-desktop" and their saved passwords. One of these desktop master keys are marked active. The third Master Key has a source of "joplin-mobile" without a saved password.
What do I do to get my encrypted Joplin Notes working again?
Joplin Windows is version 1.7.10 (prod, win32) while the Android version is 2.0.2
At this point it might be easier to export (backup) all your notes on the desktop, then delete all local copies and the sync target. Delete the Joplin app from your Android altogether.
Restore the backup, enable encryption and sync back to the server, then install Joplin back on your Android... Last step would be to enter your encryption password since there should be only one key by then.
On Windows the files are in %appdata\username\.config (I think, I'm not at my computer ATM). Edit: the files are in Users\yourusername\.config\joplin-desktop
I'm usually the cautious type, so I would recommend you copy the Joplin folder out rather than just delete it
Same with the sync target, if you use Dropbox, the files are in Dropbox\apps\Joplin and I'd move those out as well, instead of just deleting.
Afterwards you can delete the old files, once your backup has restored successfully.
I followed your instructions to do a clean install, but I got the error "Error URL invalid". Fortunately, I found a solution to this Onedrive specific error at OneDrive Sync issues
My Joplin is working again encrypted. Thanks again