To redeem a promo key, you'll first need a WTFast account with verified payment details (such as a credit card or PayPal.) After you've created an account and verified your payment details, you're ready to redeem your code.
Go to wtfast.com and select Account from the top menu:
Sign into your account:
Click on Enter Key and enter your promo key below. Then click Submit:
Enjoy your bonus WTFast Premium time!