[tamborine]

I just saved the offer to paypal, then went right to google play and bought my book. I didn't look for an email. You have to make sure, though, that when you purchase something you change your payment method to paypal in google play. There's a dropdown right on the page where you're purchasing the item.

eta: I just checked my email. I never received an initial one from paypal, but I received receipts from both paypal and google. The google one is for the full price minus the google opinion credits ($10.69 - $2.81 = $7.88), and the paypal receipt subtracts the $3.00, showing that I paid $4.88 for the book.