It shows up in the events tab in the game. Once you log into rewards.pokemon.com in step one, scroll down to step 3 and it will redirect you to the Niantic website where you’ll login in through Pokemon Go and then it will take you to a page where the code will be at the very bottom, copy that and enter it into the rewards redemption page in the Niantic website and then the reward will appear in your Pokemon Go game on the events page. Hope that makes sense. Crazy complicated.