If you're unable to list on eBay since Mai 11 it's probably because of the changes that eBay have made to the categories. They removed all the sub-categories for specific sport like Baseball, football, etc and grouped everything under one master category for sports cards singles. They also have done the same for non-sport cards and for gaming cards.
In the Kronocard message center you will probably get something like this:
Error: 21920203: Return policy option deprecated. The value specified is no longer supported in certain categories or sites.
Error: 21920208: PayPal not applicable for managed payments. This selling account is enabled for payments managed by eBay. PayPal is not currently accepted as a payment method and has been removed from the listing.
Error: 21916883: Invalid condition id The provided condition id is invalid for the selected primary category id.
Here is a patch you can apply to fix the issue: Kronocard-Patch-May-2021
To do this manually, you need to select the category that is no more working and all the categories that you're listing in, change the category code and also the condition code. As the exemple in the image, we selected Baseball, change the category code to 261328 that will also be the same for all other sport cards. After that, for the condition you have two choices, no condition or used. In our case we prefer to have no condition information than having the word Used... But the choice is up to you.
If ever you're are unable to fix it yourself, let us know at support @ kronozio.com and we will be happy to help you with this issue.