Was getting the same error on two devices trying to download an in-app upgrade purchase. Tried all sorts of fixes including contacting Google Play support. Turned out that this was a newbie error: I hadn't set up a wallet/credit card for the Google account I was using. Wish the error message had actually said that!
Useful troubleshooting was to try to download a free app from the store successfully and then fail with a paid-for app.