A small number of users are currently experiencing this problem.
After activation Epic are taking up to 30 minutes to actually display the product in your account at the moment, some users have had to wait an hour.
If a product is successfully activated you will see 'Activate on xxxxxxx' from within your Fanatical.com order page. Before opening a ticket, after activation we recommend you log out of your Epic Windows games client and then re-login, you should find the game then appears correctly.
If you still don't see the game after one hour and after logging out then logging back into Epic then please open a support ticket and let us know.