job-not-found

No job with that id belongs to this account. The same answer covers a job that never existed, one that passed its 48 hour retention, and one belonging to somebody else, because telling those apart would confirm which job ids are real.

{
  "type": "https://webkitapi.dev/errors/job-not-found",
  "title": "Job unknown, expired, or owned by another account",
  "status": 404,
  "detail": "..."
}

The API reference has the request shapes, and the error index has the rest of the codes.