When making changes in eBay store's account information, the error occurs due to the problem in refreshing eBay store token.
To solve this error, please proceed the below steps in Ship&co application.
1. Delete eBay store from 'Your shops' menu in the Shops page inside Ship&co application
2. Re-add eBay store from 'Add a new shop' menu
By above steps, the synchronisation issue will be solved.
In case that the issue is not solved with above actions, please contact Ship&co support.
Also, shipping label information of orders, that was created before re-adding the shop and was not mark as fulfilled might not be synced automatically after deleting & re-adding eBay store. In that case, please fulfill that order manually by changing order status to 'shipped' in eBay and adding the tracking number.