Cannot add user in preferences

I am trying to run version 8.4.1, as the newer version (9.9.2) appears to have issues with certain features. However, I am now unable to add my eBay user account. I get the error below, or it just hangs up. Any ideas? I can’t ADD OR refresh a token. I have tried uninstalling and reinstalling. I get to where I put my account password in, and then the below happens. I am running OS Mojave 10.14.6. I noticed I could not refresh the token on version 9.9.2 either. I get as far as this: Review and Grant Application Access: then the error

{“error_id”:“unauthorized_client”,“error_description”:“The OAuth client was not found.”,“http_status_code”:401}

Versions older than GarageSale 9 are not compatible with eBay’s changes of the authorization process. You won’t be able to fetch a token from eBay with version 8.4.1 at all.

Please also note that the current eBay authorization process doesn’t work well under older versions of macOS like macOS 10.14.
I will reply to your support ticket and try to provide you with a workaround for GarageSale 9.9.2.