Cancel the sale - you can do this using the reason 'out of stock/damaged'.
When you cancel the buyer will be refunded.
You will get a defect on your selling account for not completing the sale.
Link below:
https://www.ebay.co.uk/help/selling/getting-paid/sellers-can-cancel-order?id=4136&st=3&pos=1&query=H...
"There are two ways to be fooled. One is to believe what isn't true; the other is to refuse to believe what is true.”
Søren Kierkegaard, Danish philosopher (1813 - 1855)
