I spent more time thinking about this. Here's an example of an error response:
```json
    {
      "status": "Payment Required",
      "category_code": "card-declined",
      "additional": "This transaction was declined by the card issuer. Customer please call bank.",
      "status_code": 402,
      "category_type": "banking",
      "extras": {},
      "request_id": "OHMf6d42cf0d63311e381e606429171ffad",
      "description": "127: This transaction was declined by the card issuer. Customer please call bank. Your request id is OHMf6d42cf0d63311e381e606429171ffad."
    }
```

There are several fields that explain the error to a marketplace:
1. `category_type`
2. `category_code`
3. `status`
4. `additional`
5. `description`

Your argument makes sense that we should be able to change *some* of the fields, but which ones should be defined explicitly and guaranteed?