Final answer:
To add custom fields to a sales form in QuickBooks, you need to enable the custom fields feature, go to the Custom Form Styles menu to select the form to edit, and customize the sales form layout to include the custom fields.
Step-by-step explanation:
- Enable the custom fields feature in QuickBooks settings.
- Go to the Custom Form Styles menu and select the form to edit.
- Customize the sales form layout to include the custom fields.