A delivery method must be selected if more than one option is available for delivery. For an administrative order, there is almost always more than one...E-Ticket, Mail, Will Call, Email Confirmation are options as one or more of these is paired with Point of Sale.
If you are processing an order for more than one event in the same transaction, you must select a delivery method for each event. If you are in Point of Sale mode this delivery method is pre-selected for you in order to expedite the process.