telephony_capability_unsupported
A tenant elected a lane the resolved carrier's adapter declares it cannot perform - principally the ADR-0023 voicemail-drop lane on an adapter declaring amd below the message_end rung. Raised at campaign launch and at the answering/originate election, never mid-call. The adapter refuses rather than silently substituting an invented machine_end_ verdict, because silent degradation here means leaving a recorded message over a greeting that is still playing. What an operator does: drop the election, or move the campaign's caller-ID pool to an account on a carrier whose adapter declares the capability; the declared flag and the gate run that proved it are both readable. P2, unbuilt - TelephonyCapabilities (packages/providers/src/vocapable_providers/telephony.py:69-83) is three booleans today and carries no amd field. Two codes proposed alongside this one were not registered. A duplicate under a carrier_ prefix was rejected so this surface keeps one vocabulary. And a recording_consent_unavailable refusal for a mark-less carrier was rejected because the state it names is unreachable by construction: 22-carrier-integration.md §2.3 is explicit that playback_marks=false is not a permission to carry traffic, so the admission gate refuses the carrier before any call reaches that branch - and a published code that can never be raised is worse than an absent one, because an integrator will branch on it.
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/telephony_capability_unsupported",
"title": "…",
"status": 409,
"detail": "…",
"instance": "/v1/…"
}