This actually has nothing to do with a license key.
What’s actually happening is the shortcodes are not set up correctly for the main registration page.
This can be fixed by setting up one page for listing events, and you can put this shortcode on it: [ESPRESSO_EVENTS]
Then you’ll also need one page for event registration, and you’ll put this shortcode on that page: [ESPRESSO_CHECKOUT]
After the shortcodes/pages are corrected, you go to Event Espresso > General Settings > Critical Pages and set the main registration page setting to match the page that has the [ESPRESSO_CHECKOUT] shortcode on it.