This API is used to update title, body, private, custom_templates and children of articles that are active. Deleted articles cannot be updated. NOTE: Children can only be added and not removed, as of now.
Update an article's custom fields
To update an article's custom fields, use the ULM with Article ID API. The ULM API has been deprecated, but may be usable if your Alation instance is on-premises or if it's on Alation Cloud Service and Logical Metadata Services hasn't been enabled yet. See the API Release Notes for more information about the deprecation and what it means.
As an alternative, you can migrate your articles to Document Hubs so you can use the Documents API or Custom Field Value API to update custom fields. See Migrate Articles to Document Hubs for more information about migration.