As I understand it, the donation is collected, the seller does not have to pay.
If when collected the payment “ bounced” as unpaid, then it is likely ebay would block you, as keeping the full amount, without paying full selling fee.
Selling fee no doubt does not apply, but the reasoning is probably still built into the system.
This tells you how paypal collects after 3 weeks.
https://www.ebay.co.uk/help/account/donating-ebay-charity/buying-selling-ebay-benefit-nonprofit-orga...