Frontend & browser·Routing and navigation
the deep link worked from inside the app and returned a 404 when you refreshed the page.
SPA fallback
Also calledrewrite to index, history fallback
A server rule serving the application's HTML for any path the router might own, so a direct request to a client-side route reaches the application instead of a missing file. Every static host has its own way to configure it, and forgetting it is the classic first deploy of a single-page application. Done bluntly it also turns genuine 404s into a 200 with an empty page, which is bad for crawlers and worse for monitoring.