Hi,
Sorry for the issues. I can help out here.
First the license key is not needed for Pro to work. That is just for automatic updates.
Also, Pro is an add on for the free version and both need to be active.
Please verify you have both the core and Pro version active in WordPress.
Also, we have this guide that starts with the installation of Pro to help you out:
New User Primer: The Events Calendar and Events Calendar Pro
It then goes through all the settings for core and Pro.
Thanks