Try clearing cache and cookies, the ol' trick of logging our completely and logging back on works sometimes too.
Switch devices and browsers. Laptop / PC and try Chrome are a good combo, try from there.
If there is still an issue contact Customer Services to send you that label.
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.
@m.virgo