Q: The sync target needs to be upgraded before Joplin can sync

The sync target needs to be upgraded before Joplin can sync. The operation may take a few minutes to complete and the app needs to be restarted. To proceed please click on the link. Restart and upgrade

I clicked and then...

Joplin upgrade in progress...

Please wait while the sync target is being upgraded. It may take a few seconds or a few minutes depending on the upgrade. The application will automatically restart once it is completed.

Error

The sync target could not be upgraded due to an error. For support, please copy the complete content of this page and paste it in the forum: https://discourse.joplinapp.org/

The full error was:

GET info.json: Unknown error 2 (503): Update in process.

Error: GET info.json: Unknown error 2 (503): Update in process. at newError (/Applications/Joplin.app/Contents/Resources/app.asar/lib/WebDavApi.js:399:11) at WebDavApi.exec (/Applications/Joplin.app/Contents/Resources/app.asar/lib/WebDavApi.js:429:10)


So what to do next?