When editing or viewing an order, you may notice three custom fields at the bottom of the Order Notes section of the Order Details pop-up or the Order Sidebar.
Simply click the blue None text to fill one of the custom fields with information, or click on previously entered text to make changes. Once you click away from the text entry field, your changes will be saved.
Right now, these are only fields for you to place information applicable to each order. Unfortunately, we cannot as of yet pull in specific information from any marketplaces (other than a "Custom Store" or an updated WooCommerce store) through their API. Thus, we recommend that you use this as an additional data entry field (such as for a PO number or the like).