Additional Field on Screen not appearing in retrieved list via API

Hello, we have a couple of Additional fields appearing in our WO Completion Details section but they do not appear in the list retrieved using the "/api/WorkOrder/additionalField" API when passing the relevant Customer ID. A number of other additional fields are retrieved but the specific, newly added fields are not listed. Any ideas why this may be the case? Note, this is in our Sandbox environment. Thanks.