Formatted Incorrectly or Not a format that Apple Books can Open

[d2dautomation]

Tried this today to decrypt a book I bought from Apple Books but it is giving me the error:

Cannot Open “[Book Name]”
It is formatted incorrectly, nor is it a format that Apple Books can open.

I did check that source file downloaded is an .epub book.

[liammkellly]

I have the same issue.
I tried opening the output file with Calibre to see if it would like it better, but it says the file is DRM protected.
If I rename the file to .zip and expand I can see the text is present though so something must have been decrypted.

[superspeed500]

DISCLAIMER: Only use for legal purposes! Same stuff as described in README applies to this "instructions".

I got the same issue at first, but I was able to get it to work on macOS 15.5 on a Intel Mac by doing the following additional steps before disabling SIP and the integrity check:

• Remove all books stored localy. Make sure you have backups.
• Remove authorization for all computers on Apple account (Can be done through Apple Music for example) NOTE: All your computers on your Apple account will have to be reauthorized!
• Reauthorize the Mac.
• Open Apple Books and download all the ebooks.
• Close Apple Books and follow the steps in the README of this repo.

I then where able to sync my purchased books to my reMarkable by first converting them to PDF using Calibre (The resulting ePub from this software doesn't work with the reMarkable for some strange reason).