doc.cheap

engine_unavailable (503)

The recognition engine did not answer within its timeout. Nothing was charged.

Cause

A scan is billed around the engine call. A credit is reserved before the image is sent, and committed only when a billable result comes back. When the engine does not answer in time the reservation is released. The balance is unchanged and no result was produced.

The message

The recognition engine did not answer in time; nothing was charged. Retry shortly.

The fix

Retry. The condition is transient, so an ordinary retry with backoff is the right response. Wait a second or two, then a few seconds, then surface the failure.

Sending an Idempotency-Key on the original request makes the retry safe, even if the first call turns out to have landed.

event_id

event_id is present on the first occurrence in a window and null on the ones that follow. The failure is worth recording; one event per request is not. An afternoon of upstream downtime would cost more events than a month's quota holds. The rate is what is recorded, not each request.

The whole catalogue, grouped by what a caller does with it, is on errors.

The response

{
  "error": {
    "code": "engine_unavailable",
    "message": "The recognition engine did not answer in time; nothing was charged. Retry shortly.",
    "docs_url": "https://doc.cheap/docs/errors/engine_unavailable",
    "request_id": "req_9e6b1f7c-2d4a-4b83-9c51-7f0ad3e8b642",
    "event_id": null
  }
}