Google Play Books fails processing .epub
Yesterday, I bought the three book package to read it using Google Play Books.
I could successfuly upload Part 2(DOM) but it failed for Part 1 and part 3.

Following suggestions from the internets I could add the failing books to my GPB account by first converting them to .mobi using Calibre and then reconverting the book to .epub though the final result loses many of the nice formatting the book has.
I'd like to look into that issue.
How can I debug the problem? Try it on my Mac?
Hi @iliakan the issue occurs with downloaded books I got after the purchase.
Everything I tried was done in Linux Mint 19.1
Whenever I tried to upload book 1 or 3 to google play books, it would never be successfully processed. I uploaded them using Chrome and Firefox and nothing changed.
I also scanned all books with EPUB checker online and in the command line. Many errors would appear.
Did you try uploading it first to Google Drive and then pulling it from there?
@jasonjurotich
Did you try uploading it first to Google Drive and then pulling it from there?
Noooppp. I've never done it that way, have you? 🤔
just go to https://play.google.com/books and go to my books, and then click upload files and then try Google Drive. I have not used it, but it should work.
We're using Calibre converter for Epub. It aims to create the most compatible Epub, but warns that it's impossible to be compatible with every reader.
This issue is not resolved yet. ePubs not working with Kindle too. Could someone suggest some workaround, or at least a compatible app?
Calibre, iBooks
@iliakan Could you please make it compatible with the Kindle app?