Why does Firebase Auth Emulator in Flutter log an empty reCAPTCHA token and then throw a network error on Android?

Below is some background and clarification regarding your issue.

What’s Happening

When you see a log similar to

FirebaseAuth: Logging in as jon.doe@example.com with empty reCAPTCHA token

this message is produced by the Firebase Authentication emulator. The emulator logs that an empty reCAPTCHA token was passed (which is expected for most email/password sign‐in flows), so that by itself isn’t an error.

The actual runtime exception

Unexpected FirebaseAuthException: [firebase_auth/network-request-failed] A network error…

indicates that your client isn’t successfully connecting to the emulator endpoint.

Common Causes & Checklist

Even though you’ve already verified a few key points, double‑check these items:

1. Correct Host Address:
   On Android, the emulator must be reached via 10.0.2.2 (or 10.0.2.2 if using the Android emulator) instead of localhost. Your code correctly does that:

   DARTCopied
   String host = Platform.isAndroid ? '10.0.2.2' : 'localhost';
   await FirebaseAuth.instance.useAuthEmulator(host, 9099);

2. Cleartext Traffic Allowed:
   Since the emulator runs over HTTP, cleartext (non‑HTTPS) traffic must be permitted in your Android manifest. Verify you have added:

   XMLCopied
   <application
       android:usesCleartextTraffic="true"
       … >

   If already enabled, check that no network security configuration is overriding this setting.

3. Emulator Accessibility:
   Confirm that the Authentication emulator is running and reachable. From your computer or emulator’s browser, accessing http://10.0.2.2:9099 should give some indication that the service is active.

4. Initialization Order:
   Make sure that Firebase.initializeApp(...) and the call to useAuthEmulator happen before any authentication methods (like signInWithEmailAndPassword) are invoked.

Summary

• The “empty reCAPTCHA token” log is a normal debug output from the emulator for email/password methods.
• The network error most likely means the client isn’t reaching the emulator. This is often due to connectivity issues (such as misconfigured cleartext permissions or emulator network settings) rather than a failure of the reCAPTCHA flow.

Double‑check the above points and ensure that the emulator’s URL (with host 10.0.2.2 on Android) is reachable from your device/emulator. Once connectivity is confirmed, the email/password sign‑in should work even though the emulator logs an “empty reCAPTCHA token.”