verification_link_invalid
The email-verification token is unknown, already consumed, or past its window. 400 rather than 401 because there is no credential to re-present: request a new link.
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/verification_link_invalid",
"title": "…",
"status": 400,
"detail": "…",
"instance": "/v1/…"
}