Take a peek through your eBay messages, email and your order details, if the code is not there, contact Customer Services, they will provide this essential code for you. Remember, you have 7 days to pick up your item, from the time you were notified that it's in store.
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 do recommend contacting CS very first thing in the morning, when the lines first open, as there's more chance of Dublin answering.
@wednesbury