Let attendees buy several of the same ticket in one checkout. This is useful for a company making a single payment for several places. To enable quantities, go to Event Settings > Event Experience > Registration & Checkout. Under Registration Settings, turn on Show Ticket Quantity Field? and select Save. This is on by default. If you turn it off, attendees can still buy different ticket types together, but can choose only one of each type.
To limit one ticket type to one per attendee, go to Ticketing & Payments > Tickets, Add-ons & Donations > Tickets. Open the ticket’s Actions menu, choose Manage Ticket, then open Checkout > Purchase eligibility and turn on Restrict to One Per Attendee?. Select Save and Close when finished.
Restrict to One Per Attendee? is part of Advanced Ticketing. If it is disabled, check whether your current plan includes that feature. The event-wide quantity setting and the ticket-specific one-per-attendee restriction are separate controls.