I have tried pretty much every code on the first page, in several countries, including India, with a new account that has never used any codes before.
I guess the book just is not coupon eligible anywhere. But I will keep trying and will keep an eye on Google Play too.
Thanks
Oh, and perkopolis didnt work either, even in Canada. I just thought it was the book I was trying to use it on, but maybe it has expired.