Google Sign-In

Enable provider in Firebase

1. Go to Firebase Console → Authentication → Sign-in method.
2. Click Google, enable it, select a support email, and save.

Add SHA-1 fingerprints (Android)

Google Sign-In on Android requires SHA-1 and SHA-256 fingerprints for your keystore.

1. Generate the SHA-1 for your build:

   cd android && ./gradlew signingReport
   

   For production, also copy the SHA-1 from Google Play Console → Release → Setup → App signing.

2. In Firebase Console → Project Settings → General, scroll to your Android app and click Add fingerprint.

3. Paste your SHA-1 (and SHA-256 if available) and save.

4. Re-download google-services.json and replace android/app/google-services.json.

iOS URL Schemes

1. Open your downloaded GoogleService-Info.plist.
2. Find <key>REVERSED_CLIENT_ID</key> and copy its <string> value (e.g. com.googleusercontent.apps.1234567890-abcdefg).
3. Open ios/Runner/Info.plist (or edit via Xcode) and ensure the URL scheme is present:

<key>CFBundleURLTypes</key>
<array>
  <dict>
    <key>CFBundleTypeRole</key>
    <string>Editor</string>
    <key>CFBundleURLSchemes</key>
    <array>
      <string>YOUR_REVERSED_CLIENT_ID</string>
    </array>
  </dict>
</array>

Replace YOUR_REVERSED_CLIENT_ID with the value from step 2.

Test

Build the app and test Google Sign-In on both platforms. If it fails with DEVELOPER_ERROR, recheck package name vs SHA-1 vs google-services.json mismatch.