Do I need to validate my EPUB before submitting it to Apple Books? How can I do this?

All EPUB books submitted to Apple Books must pass the most recent version of EPUBCheck. Various validation tools exist for this. One of the easiest and most comprehensive is the International Digital Publishing Forum's free online EPUB validation service.

I validated my EPUB file and got errors. What do they mean?

Take a look at the explanation of errors by the developers of EPUBCheck.

Where can I download the Apple Books Store Asset Guide 5.0 with information about EPUB 2 books?

The current version of the Apple Books Asset Guide contains information about EPUB 3. However, if you still need access to the documentation to create EPUB 2 books, you can download Apple Books Asset Guide 5.0.