1. Before redeeming a promotion code, make sure to link an email to your game account in the game. You can do so by pressing the "Leave e-mail" button in the game settings. You will not be able to redeem promotion codes without linking an email and stating the correct linked email in the form.
2. Make sure that the promotion code you're redeeming is still valid and not expired. Expired promotion codes cannot be redeemed.
3. All promotion codes can be redeemed only once for one account.
4. Rewards for redeeming codes are sent to the in-game "Rewards" section and are stored there for 30 days. Don't forget to log in and claim them!