Hi there,
From your system information, it does not look like Events Tickets Plus is installed.
A few things to check. Make sure you also have Event Tickets installed and active. Then, install and activate the Events Tickets Plus plugin through the WordPress “Plugins” interface. Once activated, you will then see the field to enter your License key in Events > Settings > Licenses.
If you tried to enter this before activating the plugin, there’s a good chance you actually entered this in the field for Event Aggregator. Since you describe seeing a notification about Event Aggregator, I’m guessing this is what is going on here.
Hope that helps! Please let me know if you have additional questions about this.
Thanks,
Sky