APIC's REST API consistently uses the same `imdata` envelope structure for both success and error responses; on failure, the array contains an `error` MO with attributes like `code` and `text` describing the specific validation/business-logic failure. This means robust automation code must always parse the response body (not rely on HTTP status code alone) to extract actionable error details - directly reinforcing the lesson from earlier questions about not ignoring response bodies.
`totalCount` is a general envelope field, not exclusive to successful GET responses (D is false), and 400 indicates a client-side request problem, not controller unreachability (C is false, that would typically be a connection-level failure, not an HTTP 400).