Have you tried a different device or browser?
Is it any sort of bladed item, for this a credit card on file is needed. Even nail clippers or a cake slice fall under this umbrella.
If you're using the app it's often glitchy and needs , it seems ( I don't use it! ) constant updates, switch if you can to a laptop / PC and use Chrome, that seems to work best with eBay.
Unless you've had dealings with this seller before and they've blocked you? 🤔
@jpweir1