In your Shopify admin page, Go to SettingsCustom data → Select an option (Products, Orders, etc) to configure the Meta-fields.

Here is an example of product meta-field:

List of meta-field definitions in product.Details of a product meta-field definition.

There are three fields in this definition:

  1. Name
  2. Namespace and key (the disabled one)
  3. Description

Take the 2nd one - Namespace and Key separated by a period or full stop (.):

Namespace: custom

Key: color

These are the values we need for the meta-field configuration in Final Invoice.

Now, go to Templates in our app → click CustomizeLine items → scroll down and check Show product meta fields → Add property and supply those values

Product meta-fields section in the line items.

Details of the product meta-field property.

Click Save template and you are good to go.