https://www.ebay.com.au/help/selling/posting-items/labels-packaging-tips/buying-printing-postage-lab...

How to cancel a postage label

If you haven't used a postage label, you can cancel it within 5 days of creating and printing the label. If your cancellation request is approved, you'll receive a credit for postage and related charges within 25 days. The credit will then be shown in your seller account activity, and on your next monthly invoice.