The required ticket (pricing option) feature in Event Espresso 4 will let you set a specific ticket to required. This means that it will be mandatory for registrant/attendee to complete registration checkout with that ticket option.
Check out the steps below and then watch the video tutorial:
Login to your WordPress dashboard (WP-admin) and go to Event Espresso –> Events. Then click on Add New or click on an existing event to edit an event that you have already created. Go ahead and enter basic event information such as a title and event description. Then create the datetimes that should be available along with the ticket options. Next, click on the advanced options (gear icon) on one of the tickets and then place a checkmark in the required ticket checkbox. Then save changes by updating the event.
Be sure to toggle full screen in the bottom corner of the video.