telephony_verification_unsupported
The account's carrier has a registered adapter that can place calls but cannot answer the two onboarding reads - prove a credential pair, prove a number is the account's. Raised at TelephonyResolver._build_provisioning_adapter, which narrows a built adapter through supports_provisioning (all three of fetch_account, find_number, aclose must be callable) and refuses here rather than letting an AttributeError surface mid-onboarding. Distinct from telephony_provider_unsupported, which means no adapter exists at all. Unreachable for the incumbent, whose adapter implements all three.
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_verification_unsupported",
"title": "…",
"status": 503,
"detail": "…",
"instance": "/v1/…"
}