Sync: Order & Order Items custom fields

The custom_field fieldtype is a special fieldtype that can read out the custom fields of a synced item. It will render a table in the Channel Entry view and has a tagpair to render the custom_fields in your HTML.

You should use

Fieldtype Tag pair

{order_custom_fields}
    {custom_fields:label}
    {custom_fields:value}
{/order_custom_fields}