I’ve added additional Custom Fields to my WooCommerce pages – will these be included when downloading an Order via the REST API?
Custom fields are not automatically included in the v1 REST API output. POST meta (custom fields) need to be added to the REST API output before they would display within that as they are not automatically passed to the API. If you are a WordPress developer or have access to one WooCommerce have recommended this website as a starting point (the WooCommerce REST API uses the WordPress Core Software REST API so changes need to be made to WordPress to enable this functionality).
The v2 REST API now returns additional Meta Data for most API endpoints including Customers, Orders, and Products. In our testing custom fields that were added to WooCommerce pages are included in the Meta Data for that endpoint (e.g. Orders). This screenshot shows the Meta Data for an Order which includes the shipping phone number field which was added as a custom field to the checkout page: