1. Open Ordering > Checkout As and select the customer (or leave Guest Checkout).
2. Click the calculator icon under the module list (requires the Custom Charge module) — the Custom Charge modal opens.
3. Under Enter the amount you want to charge type the amount (the field accepts 1 to 10,000) and fill in Charge Description.
4. Click DONE — the charge is added as a cart line; click the line later to edit amount or description.
5. Press Charge $X, complete delivery/pickup info if the cart needs it, and take payment as usual.

On the resulting order the charge appears in a Custom Charge section (the title is configurable under Order: Custom Charge > CustomCharge: Title) with its description and value, and it can be refunded per line.