When money is not in the Available section of your Payment Summary to make a refund, eBay do use your back up source, a credit or bank card to make that payment.
Use a laptop / PC and Chrome not the app and add that card here:
https://ppcapp.ebay.co.uk/myppc/wallet/list
If there are still issues contact eBay Customer Services to add those details for you.
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.
@jama411950