Tickets - Maximum
This is the maximum number of tickets you would like the customer to be allowed to purchase for this ticket type.
The default value for this field is 0, meaning the customer can purchase any quantity (up to the Event Ticket limit set in Event Settings).
If you would like to sell something such as 2 / 4 / 6 / 8 tickets then set this minimum to 2, set the maximum to 8 and set the "in groups of" to 2.