Add a service charge

Quick Widgets is not on the App Store.

Steps

Open the page that lists every widget and turn on the service charge.
Place it in the theme on the product that should offer it.
If that product is out of stock, the theme editor warns you. Do not offer the service on a product you cannot sell.
Add the product to the cart and confirm the charge appears as you configured it.
Leave the custom checkout field for an order note. Do not ask for personal details there.