spend_state_unknown
Launch refused: the tenant has a spend cap and the period's ledger holds chargeable usage on a meter that reaches an invoice but that its Plan carries no overage_rates entry for, so period-to-date spend cannot be established. The detail names the meter, the plan, and the period start. Fail-closed per 11-billing.md §Enforcement - unknown spend state does not launch. Price the meter on the plan or clear the cap; bundled and internal meters never raise this, because no plan prices them.
Problem shape
Every non-2xx response is an RFC 9457 application/problem+json body. The type URI below is stable and machine-matchable, so branch on the final path segment (the code) and treat the status as redundant confirmation. See the error-handling guide.
{
"type": "https://docs.vocapable.com/errors/spend_state_unknown",
"title": "…",
"status": 409,
"detail": "…",
"instance": "/v1/…"
}