HTTP status codes / 4xx — Client error
404 Not Found
What it means
The server has nothing at this URL. It does not reveal whether the resource ever existed or might exist later.
What causes it
Typos in the URL, deleted or moved content without a redirect, case-sensitive paths, wrong environment (staging URL against prod).
How to fix it
Check the URL character by character (and its case). API calls: verify the base URL, version prefix (/v1 vs /v2), and resource id. Site owners: add a 301 from moved URLs; watch Search Console for 404 reports.