Since ARMA 3 is on Steam instead of Origin, we have to use a little different process to get it. The good news is that it's actually easier. So, check my previous post- the directions are the same up to step 5. Then...
- On PrizeRebel, go to Prizes.
- Select "Custom Order" from the menu on your left-hand side under "Prize categories."
- Use the drop-down menu by "Merchant" to select "Steam Game."
- Paste Arma 3's URL (http://store.steampowered.com/app/107410/) and the other info into the appropriate boxes and hit submit. PrizeRebel will gift the game to you- check the email account you used to sign up for Steam with. You will get an email from Valve saying that the game has been gifted to you.
- Go play some ARMA 3.
- Go to Prizes.
- Search for "Steam Wallet."
- Claim your Steam Wallet card, input the code into Steam (under the "Games" menu), then use it towards the purchase of ARMA 3.
PROTIP: This process works with ANY steam game.