Additional tickets or products can now be added to a customer's existing transaction, and items added to the transaction will be included on the customer's original ticket QR code. When you're in the customer's transaction details simply click the "Add Items to Transaction" link option - see screenshot below:
After clicking on Add Items to Transaction, select an event from the dropdown, click Continue and then Add Items. This will pop up the event page to complete an admin sale. You will be able to process the order by entering the cardholder's payment details, as comp order without payment, or issuing an invoice for the customer to pay later.
As mentioned above, all new items will be added to the original transactions and ticket QR code. For payments processed up front or comps the tickets will be added immediately. For invoices you will have the choice to add the tickets immediately or wait until the customer has processed their payment. More info on invoicing can be found here.