Are you trying to pay today?
Friday especially in the morning here in the UK , is eBay's maintenance day, and many things are not possible from time to time.
This is when the techies in eBay's HQ in CaliforNIA are tweaking and installing new systems and making things go awry a little here, from time to time.
Try again a little later on hopefully, things will be back to norm.
Otherwise , if this has been happening in the past few days, try changing devices or browser. Switch if you can to a laptop / PC and use Chrome, see if that helps.
If not, 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.
@maclaughlin2006