Use a laptop / PC and use Chrome, don't use the app or mobile browser, then add the card you wish to use for refunds here:
https://ppcapp.ebay.co.uk/myppc/wallet/list
It may take a few days to verify those details.
If there's still an issue you'll need to contact eBay Customer Services.
This is the easiest and quickest way to contact eBay Customer Services, for a Call Back option.
https://www.ebay.co.uk/help/eua?id=5275&mkevt=1&mkpid
Lines open 8 a.m. - 10 p.m. on weekdays
9 a.m. - 6 p.m. on weekends.
Automated agents will be available on chat outside of the above hours.
I recommend contacting CS first thing in the morning as there's more chance of Dublin answering.
@thebikebitsstore