The immediate problem I have encountered is described here, but I'm interested in the general concepts which apply in situations like this. What happens if a paid app stops working after an update? Google Play store provides no way to revert an upgrade, and according to their ToS a refund is only possible within two hours after an initial purchase:
As a courtesy to our users, Google offers a full refund on apps and games purchased on the Play Store if the purchase is returned within 2 hours. You can only return an app or game once for a courtesy refund.
Afterwards, Play Store recommends contacting the app developer. In my case the app developer doesn't seem to provide any ToS on their web page.
Does the developer have any legal grounds to refuse providing me a downgrade / refund?