To sync your Calendar with Eventbrite take those actions:
Double click on the Calendar to open the Settings.
Click on the Add-ons section.
Open Add-ons Store.
After adding to your site, connect to Eventbrite.
After clicking on Connect, sign in or sign up Eventbrite and with the next step click on "Allow" to connect your Eventbrite with Calendar.
To finalize your actions, enable synchronization, and choose sync method Auto or Manual. If you want your events to be populated automatically your can choose Auto option. Or you can choose Manual option and choose the events that will appear on the Calendar.
You can sync your calendar both in Free and Premium plans. But note that in the Free version of the Calendar only 10 events can be displayed. So the calendar will sync only as many events as there are left on your event limit. Whereas with the Premium versions calendar will sync all the events.
All the events that are auto synced from the external calendar are not available in our Calendar settings. So, you should modify your synced events only in Eventbrite Calendar settings.