If it's not in your eBay messages, email look into Spam too, or in your order details, then you'll need to contact Customer Services, they'll provide this essential code for you.
Be aware, you have 7 days from when you were informed the item is at your collection point, to collect your item.
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.
@arl4-91