Because the official method is defunct, the community has developed workarounds to bypass the server check and unlock all levels:
Version 1.5.1 was the final official update for the Windows platform before Rovio discontinued PC support. To access premium content like the Field of Dreams bad piggies 1.5.1 activation key
Would you like a guide on recovering past purchases from Google Play or the iOS App Store instead? Because the official method is defunct, the community
This is the most reliable method for version 1.5.1. It uses a small Python script to simulate a server response, tricking the game into thinking it has been legally activated. You can find the RovioActivationScript on GitHub. Because the official method is defunct