Errors

Every error responds with the same envelope:

{
  "error": {
    "type": "invalid_request_error",
    "code": "parameter_invalid",
    "message": "url must be http(s)",
    "param": "url"
  }
}

HTTP	type	codes
401	`authentication_error`	`missing_api_key`, `invalid_api_key`
404	`invalid_request_error`	`resource_missing`
405	`invalid_request_error`	`method_not_allowed`
409	`invalid_request_error`	`resource_archived`, `idempotency_conflict`
422	`invalid_request_error`	`parameter_invalid`, `parameter_missing`, `parameter_unknown`
429	`rate_limit_error`	`rate_limited`
500	`api_error`	`internal`

Notes:

Validation errors are 422 (not 400): the request was well-formed but a value was refused; error.param names the field.
resource_archived (409) protects intent: an archived source stays archived until you explicitly restore it — a sync must not silently resurrect something an owner removed from their agents. The message includes the restore call.
DELETE answers 405: sources are never destroyed, only archived — history (citations, conversations that used the source) stays intact.