The game now moved from beta to release. There are two versions on Google Play: -lite- and -full- and there is no in-app-purchase anymore. The free lite version has a few maps for free and no campaign while the full version has everything included (all maps, campaign etc.).
Important: If you participated in the closed beta or if purchased any number of maps during the beta, just keep the lite version and it will behave like the full version for you for free (if it doesn’t work for you like this, write an email and I fix it). That is a gift for your support during the beta!