Here is a video that illustrates this process. Written instructions are below...
Here are the steps for registering Notion if you received a boxed copy of the software or a code from a 3rd-party dealer:
1. You will want to go to my.presonus.com and create an account.
2. Log into your account, press the "Register a Product" button, choose "Software or Extensions" from the drop-down, and enter your product key.
3. Once you register Notion, the program will show up in your account under "Products."