Creates or updates a Contact, matching on the email address. If the Contact does not exist, it will be created. If the Contact does exist, it will be updated. It is not possible to delete a Contact via this endpoint. It is not possible to reset properties of a Contact by passing empty values. E.g. passing null for first_name or an empty array for tag_ids won't update previous values. To do that you would instead need to use the Update Contact endpoint.