This is my first time to publish my book on Google Play Books. I already publish on Amazon without any problem. Then, I use Calibre to convert my ebook to ePub format, and upload to Google Play Books. There is an error:
Unable to sanitize epub
I did look in Google forum, but it didn't help.
I found the way to fix that issue:
First, validate ePub file in: http://validator.idpf.org/
We can see some problems in there. And we need to fix it.
Second, use Calibre to edit ePub file (Right click to the book -> Edit book)
We can see a lot of HTML files, CSS files,... Please follow the errors that validator warn, and fix it.
Save it, and upload to Google Play Books again.
That's solved!