Learn how to add keys to a Campaign
You can add keys to a Campaign by going through the Campaign setup process. On the last step, you will see a tab called Creator Kit. It is here that you add the keys for your Campaign.
Once you get to this section, you will see a section called Code. Here you will be able to add different platforms depending on your game. To add a platform, simply press the Add Platform button and choose which one.
After selecting the right platform, you can add your keys to the text box. One key per line is enough for the system to distribute them. 
On the bottom of the Code section, you'll notice a button called Add Code Set. This can be used to give out additional keys to Creators (for example, you have a multiplayer game and want them to play with friends). Another use for Code Sets is including DLC in the set so that when a Creator is accepted into the Campaign, they get the key for the game and whatever DLC you want them to have as well.
You can add keys to your Campaign at any time by going to your Campaign and pressing Edit Campaign, and finally navigating to the Creator Kit section and adding more codes to the key sections.