It could be an eBay glitch, another member posted about a similar message earlier today
Have you tried the usual (clearing cache etc/ trying another browser?)
Are you on the app or the full site?
Are you trying to pay from the cart?
Have you contacted the seller to see if other buyers have reported issues? (*could* be something on their end too)
eBay do not read here (including their tech staff, despite them claiming they do 'check' here for issues) so if you keep having the issue, and want to let eBay know about it, you will need to contact them by going to 'eBay Help' at the top of any page and follow the prompts
