Are you an existing Optus customer who has changed to an eligible plan? You can see if your new plan has been activated by checking the plan name in the usage section of My Optus app or My Account. Once your eligible plan has been activated you may need to wait up to 4 hours before you can log in to the National Geographic App. 

If you've been using the 30-day free trial and are now eligible for the included app, uninstall and download the app again before logging in as an eligible customer.