It’s strange that refreshing the eBay access token doesn’t fix this eBay error.
However, I found an old thread in the eBay discussion board. This worked for someone who had a similar issue:
• Go to “My eBay” on the eBay website.
• Find the “Site Preferences” there. Then find “Third Party Authorizations”.
• GarageSale should be listed there. Try to remove it from there. There might be an option like “Revoke this authorization”.
• Next, restart GarageSale and fetch/refresh your eBay access token.
• Afterwards check if it re-appears in “Third Party Authorizations” on the eBay website.
• Try the GarageSale scheduler once again.
I can’t promise anything but maybe this works for you as well. Please let me know if that solves the issue for you.