This help doc and video demonstrate how to set the maximum quantity of tickets a patron can order for both general admission and assigned seating events.
Note:
The Max Qty setting for General Admission tickets controls the quantity shown in the dropdown menu, not the purchase limit per transaction.
For example, instead of the default 10 tickets, you may want to display up to 50 tickets in the dropdown menu.
To limit the number of tickets a patron can purchase per transaction, go to EVENT DATES within the event and adjust the Limit Qty Per Section field.
This setting limits the number of tickets a patron can purchase per online transaction for both general admission and assigned seating events.

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DEMO