You cannot actually do that any more.
Get in touch with Ebay Customer Services and ask them to mark the item as unpaid - otherwise you will be reminded to send it and your buyer may not be able to pay.
The link should get you an online chat or a callback.
https://www.ebay.co.uk/help/eua?id=5275&mkevt=1&mkpid
"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)
