Here's how to go about redeeming voucher: 1. Head over to the BioShock Infinite page on Green Man Gaming. 2. Click "Buy now". 3. Go to your basket and begin the checkout process. 4. Paste your voucher code and watch the price tumble to £1/$1/€1. 5. Complete the checkout process to receive your game key. 6. Redeem your game key on Steam.