This error is returned by eBay when synchronising products to a different account than the one originally used.

If you have changed the eBay account in the module to a different one, make sure that you have closed and disconnected all listings synchronised in the module as the
as the products will have to be published from scratch.
If the eBay account is the same, the problem appeared as a result of the ‘new API token’ request and the browser used for the request is used
usually used to log in to multiple eBay accounts, be sure to run the request again after logging out of eBay and/or repeat
the procedure from an incognito browser session because the new token request procedure (introduced starting with module version 6.6.0)
may not require you to log in to eBay if you are already logged in.