iBook purchase disappeared

I had purchased and had read a significant portion of a book in the iBooks app. I wanted to read it on my iPad, but found it was not on my iPad. I toggled various buttons on and off to try to get the book to sync between devices. It didn’t work and when I went back to my iPhone where I had purchased the book, it had disappeared from both my library as well as from my recent purchases. Any suggestions how to fix this?