Unless you have the complete book file and add to your environment for distribution by selecting Books-> List-> Internal I don't see the method above working for you. Do you have your workspace one environment configured for the VPP Managed Distribution under Settings-> Devices and Users -> Apple-> VPP Managed Distribution? Do you have an apple business manager account? Do you have your apple business manager account set up for your workspace one environment? Under the Apple Business Manager Account have you set up Content for apps and books and Custom Applications? Here you select the book you purchased, # of Licences and assign it to your WorkSpace one environment for distribution . When you sync the purchases under Workspace one you will see the order and number of licences available under Apps &Books -> Books -> List view -> Purchased. From here you would add your assignments by selecting the book and assigning. Or you could choose the redemption code method under Apple Business Manager and download the csv file then upload into your environment. This is the only reliable method I have used.