This guide substitutes your project URL and key directly into the code above, rather than reading them from a `.env` file. Mobile apps don't get environment variables injected at runtime the way a bundler-based web app does. You'd need a build-time mechanism specific to your toolchain, such as `--dart-define-from-file` for Flutter, an `.xcconfig` file for iOS, or a `Gradle` `BuildConfig` field for Android. That's a good next step once you're past this quickstart, so your keys aren't committed to source control.