Oh... That's not good. Let's knock out the basic questions while we wait for @DavidBVal , The Developer, wake up (depending on where you are in the world, it's the middle of the night right now).
1) Platform? (phone, PC, etc)
2) Where did you buy it from (Steam, Apple store, guy from an alley).
3) What's the exact error message popping up?
Google Play might not realize you're on a new device. There's a fairly common problem with Google Play not updating to a new device. You may have to go into your Google Play settings to update the info -- often by clearning out the info or manually telling Google Play it's a new device. Google Play FAQs would be the best place to find exact steps on how to do that.