Service is healthy.

The request could not be processed as written: malformed JSON, a schema
violation, an unknown property, an unknown path, an unsupported Accept
value, an invalid sector or area ID, an area type the endpoint does not
allow, an unavailable year, or an endpoint-specific constraint (for
example a multi-regional request to econbase, bulk, or
batch_requirements, each of which rejects it explicitly).

Served as text/plain.

The service has no usable data: either no dataruns are present, or a
datarun contains no years. Served as text/plain.

The request could not be completed. The body carries a diagnostic
message and is served as text/plain.

This is also the response to a multi-regional request to a service that
does not support multi-regional models.