Downloaded a book from itunes, works on iphone6, but will not open on ipad air. "not formatted correctly ". Any ideas ?

Hello colinOxford0917,

I'm sorry to hear you are having these issues with iBooks on your devices. If you continue to have issues opening the book in question on your iPad Air due to a format error, you may want to try deleting the copy on your iPad, then redownloading it directly to your iPad from the iBook Store. You may find the information and steps outlined in the following articles helpful:

Frequently asked questions about iBooks - Apple Support

iBooks: Tips for managing your iBooks library and storage on iOS devices - Apple Support

Regards,

- Brenden