telephony_provider_not_conformant
The account names a carrier whose adapter exists but whose conformance gate is not green on the current build - offline Tiers 0–4 red in CI, or the Tier 5 live observation older than a quarter (22-carrier-integration.md §1.1). Split from telephony_provider_unsupported deliberately: we have no adapter and we have one we have not proven are different operator problems and only one of them is fixed by a CI run. What an operator does: run the gate for that provider and read which tier failed, or schedule the live run against the real account; a tenant sees an account that will not dial and a reason naming the provider rather than a rotated-credential error. There is no override and there should not be one - this refusal is what makes gate G6's "tested and parked dormant" mean something. P2, unbuilt, and it lands only when a second adapter does.
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_provider_not_conformant",
"title": "…",
"status": 503,
"detail": "…",
"instance": "/v1/…"
}