DubWars currently sells for $9.99 on Steam.
How to get:
1) Link Amazon Prime and Twitch accounts
2) Click crown symbol at top of most twitch.tv pages (like here)
3) Click "Claim Offer" button under DubWars game (can collect other loot same way if you wish)
4) Follow steps they give you to download, install, and run Twitch desktop app