HTTP 409 — Conflict
4xx Client Error
What it means
The request conflicts with the current state — a duplicate unique key, or an edit based on a stale version.
What to do about it
Fetch the current state and retry, or implement optimistic concurrency with ETag and If-Match.
Where it sits
409 belongs to the 4xx family: The request contains something the server will not or cannot process. The fix is normally on the client side.
HTTP/1.1 409 ConflictChecking it yourself
# see the status code and headers only
curl -sI https://example.com/path
# follow redirects and print each hop
curl -sIL -o /dev/null -w "%{http_code} %{url_effective}\n" https://example.com/path
# JavaScript
const r = await fetch(url);
console.log(r.status, r.statusText);