Before starting with Phone Authentication, ensure you have followed these steps:

1. Enable Phone as a Sign-In method in the Firebase console.
2. Android: If you haven’t already set your app’s SHA-1 hash in the Firebase console, do so. See Authenticating Your Client for information about finding your app’s SHA-1 hash.
3. iOS: In Xcode, enable push notifications for your project & ensure your APNs authentication key is configured with Firebase Cloud Messaging (FCM). To view an in-depth explanation of this step, view the Firebase iOS Phone Auth documentation.
4. Web: Ensure that you have added the domain of your application on the Firebase console, under OAuth redirect domains.

Note; Phone number sign-in is only available for use on real devices and the web. To test your authentication flow on device emulators, please see Testing.