Confirm the route exists in the release
Open the same path through the site's own navigation and compare it with a direct browser request. If navigation works but a direct request fails, the hosting layer may need route handling for that application type.
Check spelling, trailing slash behavior, and language or slug segments against the generated route list. A route can be valid in development but absent from the production build if its parameters were not generated or its content is missing.
Fix routing at the correct layer
For a static site, configure the host's documented fallback or rewrite only when the app expects client-side routing. For a server-rendered app, ensure the request reaches the application rather than serving a generic static 404.
Avoid a broad fallback that turns every missing URL into a successful page; it can hide broken links and create misleading status codes. After adjusting routing, test known pages, unknown paths, and refreshes on nested URLs.