What is an eBay Access Token?
eBay' Access Token is like a special password that allows 3Dsellers to connect to your eBay account as a third-party app.
eBay requires you to refresh, or re-activate your token every so often. After a while, the token will expire automatically.
If the token is expired or has been removed, most features on 3Dsellers will stop working.
How to refresh your eBay token:

There are two options to refresh your token with 3Dsellers. You can either:
use eBay to log into 3Dsellers,
or, visit your eBay accounts use the Refresh button in the Actions column.

How do I manage tokens on eBay?
If you need to delete tokens, visit this page on eBay.