I imagine it's because you're trading on a private account. Private accounts are only for those selling off their old no-longer-wanted possessions from wardrobe and attic. Anyone who makes, grows, refurbishes, or buys in (new and used) items to sell, is a business and must be registered as such. Not only an Ebay requirement but the law. For confirmation, go to Ebay's Seller Centre (link at foot of any page). For full information, go to the government's website.
Note that there is no such thing as a 'hobby seller' in this country, and how much or how little you sell or make is totally irrelevant. You could be making a loss, but you're still a business and must be registered as such.
Note too that consumer law states that customers of an illegally-trading seller can obtain a full refund on request for any reason whatsoever, for up to one full year and 30 days. And if the seller wants the item back (which could be battered, broken and totally useless by then), he will have to pay the return costs too. The law doesn't reward those who break it. In other words, you're currently a free hire shop for savvy shoppers!
So best to upgrade your account from private to business (takes seconds) as a matter of urgency, before you find yourself in deep doodoo with Ebay (for defrauding them of listing fees) and Trading Standards (for denying buyers their legal rights).
@fewthings22
