If you purchased either a physical retail or a direct download version of Civilization Gods & Kings and are getting an error message on Steam stating the code is invalid or already used, please follow the steps below:
1. Reboot Steam
2. Once Steam is reopened, on the top bar click on Games > Activate a Product on Steam.
3. Click "NEXT" at the bottom of the new window.
4. Click "I AGREE" at the bottom of the Steam Subscriber Agreement window.
5. Enter the Product Code is in field. As the code is 15 digits, the code can be enter in either of the following formats:
XXXXX-XXXXX-XXXXX or XXXXXXXXXXXXXXX
Once the code has been entered, hit the "NEXT" botton.
6. If the code entry was successful, follow the remaining windows to proceed with downloading the game.
If the code entry was unsuccessful, we would like for you to open a ticket with Steam Support (link to their support site provided below). Steam Support will be able to take a closer look at your Product Code and provide steps on what can be done next.