call_flow_test_carrier_unavailable
The line's carrier account has no usable credentials (409), or this server cannot receive carrier callbacks (503). Nothing was dialed.
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/call_flow_test_carrier_unavailable",
"title": "…",
"status": "…",
"detail": "…",
"instance": "/v1/…"
}