If you own a Chromecast or Android TV, you'll want to check out the latest offers, which earn you $6 in Play Store credit. You'll be able to redeem the promotion twice if you have two devices, earning you $12 in credit to grab some new apps, games, movies and more. Redeeming the credit is pretty simple, and there are two ways to easily accomplish this. The first one is heading to this site using Chrome on your desktop computer.
Second option is through the Chromecast app. Simple launch the app, click the gear icon, then tap the three dot overflow menu and then Check for Offers. After this, scroll to the $6 credit, tap redeem, and the money will be added to your account.
Source: Chromecast Offers