Flip-Book in an EPUB not working

I created with PubCoder an epub which contains a flip-book, using turn.js. The flip-book is embedded into the Pubcoder file, within an iframe, as suggested by PubCoder. The embedded folder has the html file and its resources. I exported the file as an epub, checked it for EPUB3 compliance and it passes. However, when I open the epub with Books, the flips-book does not show up. If I open the epub with Adobe Digital Editions the flip-book works as intended.

I am working on a iMac(2015) with macOS Monterey version 12.7.6.

Can anybody give me a hint how to solve the problem?