could not sync to google playbooks

hi, my boss has a problem with google playbooks.
books that he bought since 25th oct, doesn't show in google playbooks, but he can still buy and read from playstore.

so i googled and and follow the troubleshooting guide :
1. i refresh google playbooks -- not solving the problem
2. i remove the account and login again -- not solving the problem
3. i clear the data on google playbooks (it was 2.05 GB data books) and tried to download the books again and other problem arise.
it said Couldn't Retrieve Google Playbooks Library from Google ...
4. i used NEW android gadgets, start new, but again i got Couldn't Retrieve Google Playbooks Library from Google problems ..

and now, i'm stuck with "Couldn't Retrieve Google Playbooks Library from Google" problems ..
it seemed google cannot sync to google play books, but can sync to others (email, calendar, playstore, etc) just fine ..

btw, i use my account to test the device, google playbooks can sync just fine ..
so i think, the problem is in my boss account ..

i've searched for google customer care or technical support but found nothing, no email, and when i phoned google indonesia (i'm from indonesia), they said they dont have customer service ..

can anyone help here?