The apple-app-site-association file decides which URLs open in your iOS app. What goes in it, where it must live on every host, what Apple's CDN serves in practice, and how to debug the link that opens Safari.

An Android App Link only works when your site publicly declares that your app owns the domain. Here is the assetlinks.json file, the manifest side that has to match it, what 12 large sites actually serve, and how to find the failure when links open in the browser instead.