How to activate a The Cycle: Frontier Season 3 Mk2 key?

Redeeming a The Cycle: Frontier Season 3 Mk2 key is really simple, just follow these steps: 

1. Sign up for a Warframe Account at https://www.warframe.com/signup (If you already have a Warframe account, go to step 2)
2. Go to https://www.warframe.com/promocode
3. Enter your redemption code in the “Promo Code” box
4. The package has now been added to your account (if you are currently logged into Warframe, you may need to logout and log back in for items to be applied to your account)

The key is not working

If you have activated the key according to the guide but the code appears not to work, please check what type of error message you receive and depending on it follow the appropriate instructions:

• My key is Duplicated / Already used
• My key is Invalid
• My key is region locked / can't be activated in my country
• My key activated a different product