Could not set unknown property 'artifactType' for extension 'firebaseAppDistribution'

I'm trying to configure my build.gradle file to upload a bundle to the firebase distribution, I'm following these instructions but when I add this statement(artifactType="AAB") inside the block firebaseAppDistribution to get a bundle file I got this error:

Could not set unknown property 'artifactType' for extension 'firebaseAppDistribution' of type com.google.firebase.appdistribution.gradle.AppDistributionExtension.

This is the code on the build.gradle:

firebaseAppDistribution {
        artifactType="AAB"
        serviceCredentialsFile = System.getenv("GOOGLE_APPLICATION_CREDENTIALS")
        groups = System.getenv("ANDROID_RELEASE")
      }

What could be the problem? I know firebase just added support for uploading bundle format files to the app distribution, I already liked the accounts for firebase and the play store, so I'm a little bit lost because this is the first time I try to do this and this feature is pretty on firebase distribution.

These are my dependencies:

• classpath "com.android.tools.build:gradle:4.0.1"
• distributionUrl=https://services.gradle.org/distributions/gradle-6.1.1-all.zip
• classpath "com.google.firebase:firebase-appdistribution-gradle:2.0.1"