[Bug] Firebase Unity SDK 12.10.1 – Java 11 Conflict with Unity 2021.3.21f1 Android Build

[elifsenakuru]

Description

Hi,

I'm using Unity Editor 2021.3.21f1 and recently upgraded Firebase from Unity SDK 12.1.0 to 12.10.1. minSdkVersion is 23 and targetSdkVersion is 34.

After the upgrade, my Android build fails with the following error:

MessageForwardingService.class has wrong version 55.0, should be 52.0

From what I understand, this suggests that some Firebase libraries (e.g., firebase-messaging) are now compiled with Java 11 (class file version 55), but Unity 2021.3 appears to expect Java 8 compatibility (class file version 52).

I reviewed the release notes but didn’t see any mention of updated Gradle, Java, or Unity Editor requirements.

Does Firebase SDK 12.10.1 now officially require Java 11?

Have there been any minimum required Unity Editor or Gradle version changes that could explain this?

Is Unity 2021.3.21f1 still supported with Firebase 12.10.1?

Thanks in advance for your help!

Reproducing the issue

No response

Firebase Unity SDK Version

12.10.1

Unity editor version

2021.3.21f1

Installation Method

.unitypackage

Problematic Firebase Component(s)

Messaging

Other Firebase Component(s) in use

App Check, Crashlytics, Analytics

Additional SDKs you are using

Facebook, Helpshift, Android

Targeted Platform(s)

Android, Apple Platforms

Unity editor platform

Mac

Scripting Runtime

IL2CPP

Release Distribution Type

Pre-built SDK from https://firebase.google.com/download/unity

Relevant Log Output

If using CocoaPods for Apple platforms, the project's Podfile.lock

Expand Podfile.lock snippet

👀 Replace this line with the contents of your Podfile.lock!

[google-oss-bot]

I couldn't figure out how to label this issue, so I've labeled it for a human to triage. Hang tight.

[argzdev]

Hi @elifsenakuru, while it does look like the build suggests that versions from Java has changed, these should still be compatible with each other. That said, I did try to test our Firebase Messaging quickstart, and so far it is working correctly. However, I did change the minimum API level from 23 to 24. This isn't mentioned in our Firebase Unity release notes, so I'll try to reach out to our tech writers to have that updated.

Is Unity 2021.3.21f1 still supported with Firebase 12.10.1?

As you've mentioned, I'm guessing not anymore, since Firebase 12.10.1 was built with Java 11, it could have compatibility issues with Java 8.

Does Firebase SDK 12.10.1 now officially require Java 11?

It seems that it only works with Java 11

Have there been any minimum required Unity Editor or Gradle version changes that could explain this?

According to the comments here. The following is the JDK version used for each Unity version.

Unity version	JDK version
6000.0+	17 (OpenJDK version 17)
2022.3 LTS	11 (OpenJDK version 11)
2021.3 LTS	11 (OpenJDK version 11)

Could you try either updating minimum API level to 24 or update Unity version to 2021.3.45f1 and see if that makes a difference?

Let me know if these information help. Thanks!

[elifsenakuru]

Hi again,

I tested the same setup with Unity 2022.3.39f1 (JDK 11), and the build succeeded with Firebase 12.10.1, even with minSdkVersion still set to 23.

This suggests that the issue might be related to Java version compatibility, since Unity 2021.3.21f1 uses JDK 8.

Thanks again!

[argzdev]

You're right @elifsenakuru, after further investigation, there seems to be a compatibility version change. I took a look into the Firebase C++ sdk, and there was a pull request which changed the version from JDK 8 to JDK 11.

I checked our Firebase C++ SDK release notes, and this wasn't mentioned. Thanks for reporting this. I'll reach out to our engineers and add this in our release notes.

That said, I don't think there's much we can do regarding compatibility issues, since I noticed newer versions of Android API has also required using JDK 11 which could only mean that we have to update our SDK versions as well.

I also did an edit on my initial reply. Kindly see the changes.

I'll go ahead and close this thread for now, if you'd like us to reopen the thread or if there's anything else you'd like us to do please let us know. Thanks!