This was fixed in the rewritten CircleCI CLI v1: the new CLI supplies a complete set of local pipeline values when validating, so a config whose workflows are all conditionally skipped now validates as valid instead of erroring. A maintainer re-ran the exact reproduction case (`circleci config valid…

The cause is a version mismatch: newer CLI versions validate by calling a config compilation endpoint that older CircleCI Server releases do not expose, so the server answers Not Found. Either update the CircleCI Server instance to a version that includes the endpoint, or pin the CLI to an older rel…