It appears that there’s a problem with 3rd party checkout on eBay, and the fix isn’t likely to happen for a week.
The issue occurs when multiple items from different sellers are placed into eBay’s shopping cart and then paid for as a single transaction. For buyers this means one PayPal transaction and one payment email for multiple items, but the cash is then routed to all the sellers who ship the goods.
What should happen is that if a seller is using a 3rd party checkout they should be excluded from the multiple payment and the buyer should pay separately.
For sellers who use a 3rd party checkout this could mean you have items paid for that are still showing as unpaid. With a fix not expected before the 18th February you’ll need to keep an eye on outstanding orders as buyers who have paid tend to be impatiently waiting for their goods at the best of times.
3rd Party Checkout is due for retirement in June this year, but in the mean time until alternative checkout flows are available it would be nice if it at least worked.