This document defines a "problem detail" as a way to carry machine-
readable details of errors in a HTTP response, to avoid the need to
invent new error response formats for HTTP APIs.

...

The data model for problem details is a JSON [RFC7159] object; when
formatted as a JSON document, it uses the "application/problem+json"
media type.

See: https://tools.ietf.org/html/draft-ietf-appsawg-http-problem-00

At least be aware of this effort -- it would be nice to have alignment on representing errors.