I can’t buy the full version of the game. I receive a purchase error.

The reason might be due to the setting of your device and the Play Market application. Please try the following:
1) Check the Internet connection.
2) If you use Touch ID to confirm purchases, for some devices, the Touch ID window does not appear when making a purchase due to an error in Google Play. As a result, the app freezes and nothing appears to happen after tapping «Buy Now». If this occurs, please place your finger on the sensor. The purchase will then be completed.
3) Reinstall the application.
4) Check if the payment method indicated in Google Play was successful for other applications. Check if there is money on the card.
5) Check the system date on your device to make sure it corresponds to the real date and time. To avoid this problem, enable automatic syncing in the date and time settings.
6) Check your device for any hacking applications. We verify purchases and such applications invalidate purchases.
7) Clear the cache of the Play Market application. Go to Settings -> Applications -> Google Play Market -> Memory.
8) Check the version of the Play Market application. If you have an outdated version of the application, update it.