on Author Help:
A Universal Book Link (commonly referred to as a UBL) is a short link that will go to a web page showing links to all the stores where the ebook or audiobook can be bought. When the user clicks on any of the links, they will go to their local site if the store has one. Such a link is useful in all sorts of situations, but especially on social media, where a long list of links looks clunky at best.
This post will explain how to set up a Universal Book Link for any book (even if you are not the book’s author).