If this was just a message you can still and try ad politely convince the buyer of where you bought the item and that 2 others were sold with no issue. Do you still have the invoice, copy it on the message.
If the buyer is not appeased and opens a return case for item not as described, you will have to accept the case within 3 days, and fully refund the buyer. It's all automatic, no human contact so no point challenging it at that point. Pay for the return tracked postage and only refund when you have the item back, you have 48 hours to do that.
Stick within those timelines and your seller performance is not affected.
You can then appeal the decision for the refund, the link below shows how.
I won't admit it's easy, and as eBay do not see the item , and do usually fall o the side of the buyer.
https://www.ebay.co.uk/help/selling/managing-returns-refunds/appeal-outcome-case-seller?id=4369
@liudcher56
