Hi,
While reviewing the OpenAPI spec, I noticed the error responses (e.g., 404, 501) only have a description and lack a content schema. This leaves the structure of the error body undefined for client implementers.

The spec already includes the RFC9457ProblemDetails schema, which is perfect for this purpose. I propose updating all 4xx and 5xx error responses to reference this schema.

For example, the 404 response could be:

"404":
  description: DID or DID URL not found.
  content:
    application/problem+json:
      schema:
        $ref: "#/components/schemas/RFC9457ProblemDetails"

This change would make the API's error handling consistent and more predictable.

Thanks.