Note: Do not enter the same field names as the API uses as standard field names. E.g. If Zendesk uses `external_id` as a standard field name. You should not enter `external_id` again as a custom field name, unless we have not provided the field name yet for any reason. This should generally not be the case, as most SaaS systems ensure themselves that field names are not the same, but better to be on the save side.