You'll also see this behavior if you have a Firebase app that can run in a browser and as an Android or iOS native app (like Ionic or React Native). If your device has the native app installed but you access the website in your device's browser and try to Sign in with Email from the browser version, your native app will pick up the attempt because it thinks the dynamic link is intended for the native app. Since the request didn't come from the native app (but rather from the browser), you'll get the "Item Not Found" page in the Play store.