slot_lease_unencodable
This code is raised on a non-customer surface (the /internal voice-runtime audience or telephony provider callbacks). It is excluded from the customer OpenAPI document and is registered here so an operator reading a log line has one place to look.
The registry admitted the call but returned no portable lease token, so the runtime would have nothing to release with. Refused rather than answered with an unreleasable admission.
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/slot_lease_unencodable",
"title": "…",
"status": 503,
"detail": "…",
"instance": "/v1/…"
}