a2p_registration_state
HTTP 409§9.17 The customer team workspace on the phone (`/v1/mobile/workspace/*`, `/v1/mobile/voice/token`)
The registration is not in a state that allows this (edit only before submitting or after a refusal; submit once; check after submitting; re-send a code only while verifying). stage says where it is.
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/a2p_registration_state",
"title": "…",
"status": 409,
"detail": "…",
"instance": "/v1/…"
}