Error handling

Incarts returns structured JSON errors and echoes X-Correlation-ID when available.

Common status codes

Status	Meaning
`400`	The request body, path, or header is malformed.
`401`	The API key is missing or invalid.
`403`	The API key is valid but cannot access the requested project or scope.
`404`	The resource does not exist or is not visible to the caller.
`409`	There is an idempotency conflict, duplicate identifier, or conflicting resource state.
`422`	The request is syntactically valid but violates business rules or retailer capabilities.
`429`	The caller is rate limited. Retry after the window resets.
`500`	The API hit an internal error.

Use idempotency keys for write requests and retry only when the operation can be safely repeated.

See the headers expected by protected endpoints.

Review business rules before retrying validation failures.