There haven't been any seller fees to pay for many months now.
Is this an old fee which needs paying? Best to contact eBay Customer Services and have this fee paid asap, so you'll free your account if you wish to buy and sell on it in the future.
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.
@christopher9793