Trouble downloading book to IBooks

I tried purchasing a book on my Ipad. The "purchase" green icon was unresponsive, so I went onto IBooks on my Mac and successfully purchased and downloaded the book.

I then went back to the IPad and tried to download the book. It apperas under my purchased books, but never downloads, I just have the black progess (or, in this case, lack thereof) bar across the bottom.

I have rebooted the Ipad. No change.

I cannot see how to download the book from the Ipad to rray and start again.

What other options pls ?