Doc page: https://docs.vyos.io/en/latest/automation/vyos-api.html

{"op":"showConfig","path":[...]} on /retrieve returns HTTP 400 with "Configuration under specified path is empty" when the path exists in the schema but has no configuration — rather than a success with an empty result. Example: ["firewall","ipv4","forward"] right after delete firewall, or any node not yet configured.

The docs describe {"op":"exists"} but not this 400 behavior of showConfig. Automation that diffs live config against a desired state has to learn this the hard way (we hit it repeatedly during clean-slate re-applies: the 400 is indistinguishable at the HTTP level from a malformed request).

Suggested doc addition on the /retrieve section: state that showConfig on an empty/unconfigured path returns 400 with that message, and recommend either probing with exists first or treating that specific error string as "empty subtree".