curl --request DELETE \
  --url https://api.box.com/2.0/files/{file_id}/metadata/enterprise/securityClassification-6VMVochwUWo \
  --header 'Authorization: Bearer <token>'

{
  "type": "error",
  "status": 400,
  "code": "item_name_invalid",
  "message": "Method Not Allowed",
  "context_info": {
    "message": "Something went wrong"
  },
  "help_url": "https://developer.box.com/guides/api-calls/permissions-and-errors/common-errors/",
  "request_id": "abcdef123456"
}