Does this help at all?
https://www.mobileread.com/forums/sho...d.php?t=118559
Personally, I mostly use Calibre for organising my library and putting books on my Kobo. When I want a book in iBooks on my iPad (eg cookbooks), I just shove the epub into iBooks on my Mac (drag and drop), then tick the appropriate box in iTunes on my Mac so that the book syncs to the iPad. (iTunes > iPad > Books > Sync Books > Selected Books > appropriate tickybox.)
Or you could put it in Dropbox or email it to yourself...