ibooks
ibooks won't open a book with my new or old Apple ID. How do I fix this?
MacBook (Retina, 12-inch, Early 2016)
iTunes if you are trying to open on your computer, iBooks if trying to open with your iPhone or iPad, you need to use iTunes to add to your library so you can see in iBooks. Click on the Sync Books and then select 'All books or Selected books' (see below for an example)