insufficient_credit - Five Nine

HTTP 402 · type payment. Every spending run reserves its full max_spend_usd against your balance before the engine dispatches anything. This request’s reservation exceeded the available balance — which is credits minus open reserves (other runs currently in flight hold their ceilings too). Nothing ran and nothing was charged.

The shape

{
  "error": {
    "type": "payment",
    "code": "insufficient_credit",
    "message": "This session asked to reserve $1.00 but the balance is $0.44.",
    "doc_url": "https://docs.fiveninelabs.com/errors/insufficient_credit",
    "request_id": "req_8fk2m1",
    "balance_usd": 0.44,
    "open_reserves_usd": 0,
    "top_up_url": "https://platform.fiveninelabs.com/billing"
  }
}

The figures are live: balance_usd is what’s available, open_reserves_usd is what in-flight runs are holding. top_up_url is where to add credit.

How to fix

Top up at top_up_url. Credits never expire.
Or lower max_spend_usd — the reservation is the ceiling you asked for, not a price; runs settle at measured actuals and release the rest. A smaller honest budget often fits.
If open_reserves_usd is the culprit, wait for in-flight runs to settle (their unspent reservation releases at terminal) — or stop one.
To get ahead of this error, subscribe a webhook to balance.low — it fires when your balance crosses your threshold, before the 402.

Reproduce it

Deterministic on an fn_test_ key with the FN_TEST_402 sentinel — same envelope, $0:

curl https://api.fiveninelabs.com/v1/sessions \
  -H "Authorization: Bearer $FIVENINE_TEST_KEY" \
  -H "Content-Type: application/json" \
  -d '{"query": "FN_TEST_402 vinyl records", "max_spend_usd": 1}'