Your organization is buying books through Apple Business Manager.

Apple Business Manager allows organizations to purchase and distributebooks(such as textbooks or reference material) using the Apps and Books section. Apple Learning states that books can only be assigned tousers, not to devices. Specifically, the users must have aManaged Apple Accountin order to receive the content. Unlike apps, which can be assigned either to users or devices, books are linked to the individual account. This ensures that digital rights management (DRM) is preserved while also protecting user access. Books cannot be assigned directly to iPhones, iPads, or Macs as standalone hardware, nor can they be tied to Shared iPad device pools. Therefore, the correct assignment criteria for books in Apple Business Manager isManaged Apple Account users.