Custom Charge (labeled Invoicing when purchasing modules) lets staff add an arbitrary charge - a one-off fee, a corrected amount, an invoice line - to a customer's order from the admin checkout, entering the amount and a description in a popup at the time the charge is added. The Order: Custom Charge tab contains a single setting, CustomCharge: Title (default Custom Charge), which is the heading shown for those charges on both the admin and customer order views.