payment_past_due
A new campaign launch or ad-hoc live call is refused once a payment has been outstanding since day 7 of the delinquency ladder (11-billing.md §Dunning). Campaigns already running finish normally - a card failure never cuts a live conversation - and paying the outstanding invoice restores launches within minutes. The detail names how many days the balance has been outstanding.
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/payment_past_due",
"title": "…",
"status": 409,
"detail": "…",
"instance": "/v1/…"
}