Pokémon GO has recevied an Android-exclusive feature that enables redeeming promo codes, allowing users to unlock items with exclusive Pokémon GO promotions. Pokémon GO occasionally offers promotional codes through our partnerships and special events. Promo codes can be used to redeem items such as Poké Balls, Lure Modules, Lucky Eggs and more.
To redeem a promo code:
- In the Map View, touch the Main Menu button.
- Touch Shop button.
- At the bottom of the screen, enter the promo code in the text field.
- Touch Redeem.
After successfully redeeming a promo code, a notification will display the items added to your inventory.
Source: Pokémon GO blog