Crashlytics found an invalid API key - AndroidStudio build

This happened to me when I updated Android Studio from 3.2 to 3.3, to fix it I just updated the

classpath 'com.google.gms:google-services:4.1.0'

to

classpath 'com.google.gms:google-services:4.2.0' 

And it worked again

You just forgot to add one line, in app-level gradle file.

apply plugin: 'com.google.gms.google-services'

this happens because when you are adding firebase:crashlytics, firebase document not have this line. so you need to add it manually. see this is firebase:crashlytics document photo.

Works fine added this on fabric.properties like this:

# Fabric properties file: app/fabric.properties
apiSecret=xx68f6074dxxxxxc11dxxx97c172e8ebf0
apiKey=xxxe76c4xxxx97e8cxxxx0135e9d46f5a2xxx

Add on .gitignore (for open source projects)

REMOVE entry on AndroidManifest.xml:

<meta-data
    android:name="io.fabric.ApiKey"
    android:value="xxx6c41xxx6ec601xxxd4xxxa2" />

Oficial documentation: https://docs.fabric.io/android/fabric/settings/working-in-teams.html