Duplicated an e-commerce but can't add it to the basket

We have duplicated an item that we already have for sale in our shop

However, when we try to add the new item to the basket, we see this error message:

Product failed internal Kentico validation when adding to basket

I can't find anything that matches this error message anywhere in Kentico's support repo's

Anyone with ideas what I can check (and where I need to check it) in order for the product to be internally validated?