You can activate Origin keys bought from RPGStash with the following two methods:
Method 1. In the Origin client.
- Log in to Origin with the EA account you would like your game added to.
- Click on the Origin menu on the top left.
- Select "Redeem Product Code."
- Enter the serial key from the back of your game manual.
- The game will be added to your "My Games" section of Origin.
After download is finished you are ready to play.
Method 1. On the Origin website.
- Go to www.origin.com/account
- Log in to your Origin account using your Origin email and password.
- Select "Redeem Product Code" in the left-hand menu.
- Enter your product code on the Redeem Your Code page.
In second case scenario you still need to wait till your game is downloaded and available in the Origin client.