The error occurs because MABS (the build service) still has the Firebase plugin registered in the app's metadata. Try these three steps:

Clear Extensibility Configurations: Go to your Module Properties and ensure there is no JSON referencing the Firebase plugin or its Git URL in the Extensibility Configurations field.

Check Shared Modules: Ensure no "Common" or "Core" module referenced by this app has a dependency on the Cloud Messaging plugin.

Force a Build Reset: In Service Center, go to the app's Native Platforms tab, change the App Identifier slightly (e.g., add .temp), Save, change it back, and Save again. This clears the build cache and forces a fresh dependency calculation.

@Amit J ,

thank you for your answer, but the app with this error, never had a dependency to the Cloud Messaging plugin in the first place.
Another new app (a different one) has.

Hi @Jeroen Vormer,

What you are experiencing can really happen, and the behavior you’re seeing is a known side‑effect of how OutSystems handles mobile plugins at environment level, especially Firebase‑based ones like Cloud Messaging.

Let me try to explain in details:

Even though your old mobile app does NOT reference the Cloud Messaging Plugin, the environment now has a Firebase / Cloud Messaging plugin installed and configured, which causes the Android build pipeline to expect google-services.json.

OutSystems mobile builds work like this: 

• Mobile plugins (Firebase, Push, etc.) are resolved at environment build time 
• Once a Firebase‑based plugin is installed and enabled in the environment: 
  • The Android build pipeline always includes Firebase Gradle steps 
  • Gradle then requires google-services.json, regardless of app usage 
• The plugin dependency is implicit, not only based on references in Service Studio

This is expected behavior, but poorly documented.

During Android build, OutSystems: 

• Injects com.google.gms.google-services Gradle plugin 
• Tries to apply: 
  com.outsystems.firebase.cloudmessaging 
• Gradle enforces: 
  google-services.json must exist 
• If missing → build fails.

Solution:

Add a default google-services.json to the environment 

Even if an app doesn’t use FCM, the file must exist. 

What to do: 

• Go to Firebase Console 
• Create / use an Android app entry (can be generic) 
• Download google-services.json 
• Upload it in Service Center → Factory → Mobile Apps → Firebase Configuration

One file is enough for all apps. Old apps will build again. New app keeps working. 

This is the most common enterprise workaround.

Hope this helps,

Cheers,

Saugat