An item you won and did not pay for inside the window. The win is cancelled, the item goes back to the store or on to the next bidder, and it usually counts as a strike.
The window
30 minutes. For a timed auction it runs from when you first open the win, and at most 12 hours after the auction ended.
That second clause is the part worth understanding, and it is there for you: an auction that ends at 2am does not quietly expire while you sleep. You get a grace allowance for a win you have not yet seen, and the 30 minutes only starts when you look.
What it is not is unlimited. Twelve hours after the end, the window has run whether you opened it or not.
What it costs
A strike. Three inside ninety days pauses your bidding. One is nothing to panic about. What is a strike?
The item. It goes to the under-bidder as a second-chance offer, or back to the store.
Nothing in money. No fee, no charge, no card taken. The cost is the mark and the item.
If something genuinely went wrong
Ask for the strike to be removed. The cancellation message says so itself: if there was a reason, you can ask for it to be removed. A failed card, a lost phone, a week in hospital — these are lifted routinely.
Do it from your strikes screen rather than starting a support request from scratch; the strike is already attached there. Can I appeal a decision?
How to not have one
Pay from the notification. Almost every unpaid win is forgetfulness, not refusal, and the notification is the shortest path to paying.
Turn notifications on, and check they are arriving. Notifications, explained
Treat a bid as a purchase. It is one. If you would not buy the thing at your bid right now, that is the bid not to place. How bidding works
Have a payment method that works before the show, not during it. A card you need to go and find is how 30 minutes disappears. My payment failed
The one that does not count
A second-chance offer you let lapse. If the item came to you because somebody else did not pay, not taking it costs you nothing — it simply goes back to the store. No strike. What is an under-bidder?
For sellers
An unpaid win is your item back, unsold, and the second-chance offer happens without you having to chase anybody. What is a second chance offer?
More: what happens if I do not pay, unpaid winner, what happens when you win.