To redeem a promotional code, please do the following:
1. Go to the settings page, scroll down and click "Redeem a code"
2. On the next page, sign in with a Google account
3. Select your Google Play account: the code will be redeemed to this account and available on all devices where you sign in with it.
4. Click "Redeem code" and enter the code
5. Verify that the product has been added
For your other Android devices, follow steps 1 and 2 to sign in and click "Refresh" to activate the promo code on the device.