Use Google Tag Manager and conversions to track specific user actions such as purchasing a Ticket for an Event.
Per Google,
The primary way to measure a Google Analytics conversion is to create or identify an event that measures the important user interaction and then mark the event as a conversion. For example, if you use the Google tag or Tag Manager, you would create the event for your website and then go to Google Analytics to mark the event as a conversion.
Use the instructions here to set up a conversion in Google Analytics 4.