DCR error response per RFC 7591 Section 3.2.2
Authorization server returns HTTP 400 with error details when registration fails due to invalid metadata or policy violations.
REQUIRED: Single ASCII error code string
Optional
OPTIONAL: Human-readable ASCII description
DCR error response per RFC 7591 Section 3.2.2
Authorization server returns HTTP 400 with error details when registration fails due to invalid metadata or policy violations.