If you try to buy something and receive the message "Commerce Unavailable" there are two possible causes. Either your device is not running Google Play Store version 3 or later or you have not configured your account.
If you are running an older version of the store you'll need to update the Google Play Store on your device. If your store icon says "Market" it is too old. It should say "Play Store".
If you have "Play Store" you probably have not setup your Google account. To do this, go to your device's Settings and under Accounts select Add Account. Once this is setup, re-start Let's Bowl 2 and try again.