voicemail_callback_not_in_service
The campaign elects a voicemail drop, but the callback number the composed message names is not an active voice number on this campaign's own telephony account with a receiving agent configured. Publish proved the tenant owns the number; this proves a callee who rings it reaches someone. It is not a warranty that the number offers the automated 24/7 opt-out an artificial-voice message is expected to carry - that duty is the customer's under the Cold Outreach & Data Provenance Waiver.
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/voicemail_callback_not_in_service",
"title": "…",
"status": 409,
"detail": "…",
"instance": "/v1/…"
}