Errors#

{
  "success": false,
  "code": "INSUFFICIENT_CREDITS",
  "error": "Not enough available credits for the maximum cost"
}

HTTP	Code / condition	What to do
202	`OPERATION_PENDING`	An admitted request is not complete yet. Poll the operation (Retry-After) before creating new work.
400	`BAD_REQUEST`	Correct invalid URLs, unsupported options or limits.
401	`UNAUTHORIZED`	Check the key or token, expiry and revocation.
402	`INSUFFICIENT_CREDITS`	Provide enough available credits for the reserved maximum.
403	`FORBIDDEN`	Check granted scopes and session-only access requirements.
403	`DESTINATION_BLOCKED`	Luni does not fetch IP lookup, IP echo or request-inspection services, including redirects to them.
404	`NOT_FOUND`	Check the route, source or owned operation ID.
409	`CONFLICT / stale execution`	Do not reuse a key for changed input; inspect the current operation.
409	`OPERATION_CANCELLED`	The operation was cancelled. Start new work with a new Idempotency-Key.
410	`RESULT_EXPIRED`	Request new collection with a new identity if needed.
413	`PAYLOAD_TOO_LARGE`	Keep the request body under 100 KB.
424	`SERVICE_UNAVAILABLE`	The source could not provide a useful result; inspect the operation.
429	`RATE_LIMIT_EXCEEDED`	Respect Retry-After and reduce outstanding work.
501	`FEATURE_UNAVAILABLE`	The endpoint or required service is not enabled.

An error can include operationId when work was already admitted. Keep it for inspection. A feature rejected before admission has no new operation or reserved budget. MCP execution failures carry a structured error and isError; protocol errors are separate from source failures.