You can add custom fields for individual line items in addition to those created for various transaction forms. This capability is supported for line items on:
To create a line-item custom field, go to the Settings tab, click Custom Fields, then find the list with
-Line appended to its name for the form to which you are adding the field. Click New Custom Field for that list:
Label, which will appear as a column heading.
Position. All custom fields appear after
Show custom field on printed documents.
Click Create to save the custom field.
This feature is automatically supported across all custom themes you can copy from https://www.manager.io/themes: