Having read your response, I have a theory…
I have yet to sign up for managed payments (I am purposely delaying). This means that my ability to amend, relist and list new items has been stopped (although existing listings remain live).
Would this therefore prevent me from using GS whilst I am not signed up? I was assuming that GS was an offline tool and that I could could create listings on my PC, without submitting to eBay. But maybe this isn’t the case…?
To update the eBay category data a valid eBay token is required.
Maybe there’s still an issue with your eBay token(s).
It might be required to renew the eBay token completely:
Remove your eBay account from the GarageSale preferences > Accounts, restart your Mac and then re-add your eBay account.
If this won’t help, please give this a try:
Quit GarageSale if running.
Open the macOS “Keychain Access” application and enter “GarageSale eBay Account” in the search field. (If you don’t find anything try it with “ebay token”.)
Right-click on the eBay account token in the Keychain and select “Delete”.
If done, restart your Mac, start GarageSale and add/refresh your eBay access tokens in the GarageSale preferences > Accounts.