Mobile deep linking not working — URL scheme and universal links setup

Deep links don't open the app, or open the wrong screen. Custom URL schemes work on some devices but not others. Universal links (iOS) or App Links (Android) fail silently.

(1) Custom URL schemes (myapp://): iOS: add to Info.plist CFBundleURLTypes. Android: add intent-filter in AndroidManifest.xml. (2) Universal Links (iOS): requires apple-app-site-association file on your HTTPS domain, Associated Domains entitlement in Xcode. File must be at /.well-known/apple-app-site-association with correct JSON format and Content-Type: application/json. (3) Android App Links: requires assetlinks.json at /.well-known/assetlinks.json, intent-filter with autoVerify='true'. (4) Test iOS: npx uri-scheme open 'myapp://path' --ios. (5) Test Android: adb shell am start -a android.intent.action.VIEW -d 'myapp://path'. (6) Common gotcha: universal links don't work when typed in Safari address bar — must be clicked from another app.

Universal Links and App Links use server-side verification files to prove domain ownership. Without proper setup, the OS falls back to opening the URL in the browser instead of the app.