Firebase Flutter Setup

Firebase + AdMob + RevenueCat Setup for Flutter

Prerequisites

• Firebase project created (firebase projects:create or Console)
• Billing account linked (gcloud billing projects link <project> --billing-account=<id>)
• flutterfire CLI installed (dart pub global activate flutterfire_cli)
• Debug keystore SHA-1 fingerprint obtained

Step 1: Get SHA-1 Fingerprint

# Windows (Chinese locale will mislabel — MD5 line is actually SHA-1)
keytool -list -v -keystore "%USERPROFILE%\.android\debug.keystore" -alias androiddebugkey -storepass android

# Verify: SHA-1 = 20 bytes (40 hex chars with colons = 59 chars)
# SHA-256 = 32 bytes (64 hex chars with colons = 95 chars)

[!CAUTION] Chinese locale keytool mislabels fingerprints — the line labeled "MD5" is actually SHA-1 (20 bytes), and "SHA1" is actually SHA-256 (32 bytes). Always verify by byte count.

Step 2: Configure Firebase + FlutterFire

# Initialize Identity Platform (required for Google Sign-In)
gcloud services enable identitytoolkit.googleapis.com --project=<PROJECT_ID>

# Run flutterfire
flutterfire configure --project=<PROJECT_ID> --platforms=android \
  --android-package-name=<PACKAGE_NAME> --yes

# Register SHA-1 via REST API (firebase CLI sha:create often fails)
ACCESS_TOKEN=$(gcloud auth print-access-token)
curl -X POST \
  "https://firebase.googleapis.com/v1beta1/projects/<PROJECT_ID>/androidApps/<APP_ID>/sha" \
  -H "Authorization: Bearer $ACCESS_TOKEN" \
  -H "Content-Type: application/json" \
  -d '{"shaHash":"<SHA1_NO_COLONS>","certType":"SHA_1"}'

Step 3: Google Sign-In — The 3 OAuth Clients

[!IMPORTANT] Google Sign-In requires 3 things in GCP, not just 1. Missing any one causes ApiException: 10 (DEVELOPER_ERROR).

Required OAuth Clients in GCP

Why CLI/API Often Fails

• gcloud and IAP API for creating OAuth consent screens requires a GCP Organization — personal accounts must use the Console UI
• firebase apps:android:sha:create CLI command frequently fails — use REST API instead
• OAuth client creation via API also requires Organization — use browser automation for personal accounts

Code Configuration

[!WARNING] The code below uses google_sign_in v6 API which is outdated. For v7+ usage (with initialize() + authenticationEvents stream), see the flutter-social-login skill.

// auth_provider.dart (v6 — DEPRECATED, use flutter-social-login skill for v7+)
final googleUser = await GoogleSignIn(
  serverClientId: '<WEB_CLIENT_ID>.apps.googleusercontent.com',  // Web, NOT Android
).signIn();

// google-services.json — add oauth_client with Web client
"oauth_client": [
  {
    "client_id": "<WEB_CLIENT_ID>.apps.googleusercontent.com",
    "client_type": 3
  }
]

Enable Provider in Firebase

# Update Google Sign-In provider with real OAuth credentials
curl -X PATCH \
  "https://identitytoolkit.googleapis.com/admin/v2/projects/<PROJECT_ID>/defaultSupportedIdpConfigs/google.com?updateMask=enabled,clientId,clientSecret" \
  -H "Authorization: Bearer $ACCESS_TOKEN" \
  -H "Content-Type: application/json" \
  -d '{"enabled":true,"clientId":"<WEB_CLIENT_ID>","clientSecret":"<WEB_CLIENT_SECRET>"}'

Step 4: Gradle Plugin Setup

[!WARNING] flutterfire configure adds plugins to app/build.gradle.kts but does NOT add them to settings.gradle.kts. This causes Plugin was not found build failures.

Required in settings.gradle.kts

plugins {
    id("dev.flutter.flutter-plugin-loader") version "1.0.0"
    id("com.android.application") version "8.11.1" apply false
    id("org.jetbrains.kotlin.android") version "2.2.20" apply false
    id("com.google.gms.google-services") version "4.4.2" apply false
    id("com.google.firebase.crashlytics") version "3.0.3" apply false  // MUST ADD
}

Required in app/build.gradle.kts

plugins {
    id("com.android.application")
    id("kotlin-android")
    id("dev.flutter.flutter-gradle-plugin")
    id("com.google.gms.google-services")
    id("com.google.firebase.crashlytics")
}

Step 5: AdMob Integration

<!-- AndroidManifest.xml — inside <application> -->
<meta-data
    android:name="com.google.android.gms.ads.APPLICATION_ID"
    android:value="ca-app-pub-XXXXXXXXXXXXXXXX~XXXXXXXXXX"/>

Use kDebugMode to toggle test/production ad IDs in Dart code.

Step 6: RevenueCat IAP Setup

1. Create project at https://app.revenuecat.com
2. Add Android app with package name
3. Create entitlement (e.g., pro)
4. Create offering (e.g., default) with packages
5. Get SDK key from API Keys page (goog_...)
6. Update Flutter code with SDK key

Step 7: Real-Device Testing Checklist

.gitignore Best Practices

# Firebase credentials — NEVER commit
app/android/app/google-services.json
app/ios/Runner/GoogleService-Info.plist

# FVM
app/.fvm/

Related skills

• firebase-auth-manager — implement user sign-in after Firebase is initialized. Firebase-flutter-setup provides the backend infrastructure; firebase-auth-manager builds the auth UX.
• admob-ux-best-practices → revenuecat-manager — integrate monetization after Firebase is set up. Use these for ads and subscriptions.
• flutter-verify — after setup completes, verify Firebase services are accessible and auth flows work end-to-end.