google_credential_invalid
The Google ID token did not verify - expired, wrong audience, bad signature, and unknown issuer are one indistinguishable refusal on purpose; the reason goes to the security log.
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/google_credential_invalid",
"title": "…",
"status": 401,
"detail": "…",
"instance": "/v1/…"
}