Hey there, let's work through this Firebase Auth initialization issue you're facing. That "missing dependency" error almost always ties back to incomplete or misconfigured Firebase setup in your Unity project for Android. Here are the most reliable fixes to try, ordered from easiest to more involved:

1. Re-import Firebase Unity SDK with Auth & Dependencies #

• Head back to the Firebase Console and re-download the Unity SDK for your project, making sure you check the Authentication module when selecting which features to include.
• When importing the SDK into Unity, ensure you select all Auth-related packages and the mandatory Firebase Core module (this is the backbone all Firebase services rely on).
• After importing, run Firebase > Validate Firebase Setup from the Unity menu—this tool will automatically scan for common configuration gaps and fix them if possible.

2. Verify Android Gradle Dependencies #

Sometimes Unity fails to sync the correct Gradle dependencies for Firebase Auth. Here's how to check:

• In Unity's Player Settings > Android > Publishing Settings, enable Custom Gradle Template.
• Open the generated mainTemplate.gradle file (found in Assets/Plugins/Android) and confirm these dependencies are present (use version numbers matching your Firebase SDK version):

  implementation 'com.google.firebase:firebase-auth:22.3.1'
  implementation 'com.google.firebase:firebase-core:21.1.1'
  

• Save the file, then rebuild your Android project to sync the new dependencies.

3. Ensure google-services.json is Correctly Placed #

• Download the latest google-services.json from your Firebase Console (Project Settings > General > Your Apps > Android app).
• Place it directly in the Assets/Plugins/Android folder of your Unity project. This file contains critical Auth configuration data—using an outdated or wrong project's file will cause dependency issues.

4. Clear Caches & Rebuild from Scratch #

Cached files can sometimes cause dependency conflicts. Try these steps:

• Go to File > Build Settings > Clean Build Folder (available in Unity 2021+; for older versions, manually delete the Build directory).
• Restart Unity, then re-import all Firebase packages if needed, and rebuild your Android project.
• For a deeper clean, back up your project, delete the Library folder, and let Unity re-import all assets (this fixes many hidden caching issues).

5. Check Unity & Firebase SDK Version Compatibility #

Mismatched versions between Unity and Firebase can lead to missing dependencies:

• Confirm which Firebase SDK versions work with your Unity version (e.g., Unity 2020+ requires Firebase SDK 9.0+).
• If you're using an older Unity version, downgrade your Firebase SDK to a compatible release, or upgrade Unity to a version that supports your current SDK.

Bonus: Enable Debug Logs for More Details #

If you're still stuck, enable Firebase debug logs to get a clearer picture of which dependency is missing. Add this line early in your code (before initializing Firebase):

Firebase.FirebaseApp.LogLevel = Firebase.LogLevel.Debug;

Check the Android Device Monitor again—you'll see more granular logs that can point to the exact missing component.

内容的提问来源于stack exchange，提问作者DannyFar94