I don't know what you were trying to do, if you tried to have a fixed layout epub that works in iBooks here are the steps to achieve that whilst maintaining validation using EpubCheck:
https://www.mobileread.com/forums/sho...78&postcount=4
If you're looking to embed fonts in iBooks use this:
https://www.mobileread.com/forums/sho...d.php?t=239520