Failed to resolve: com.google.firebase:firebase-core:11.2.0

Add maven { url "https://maven.google.com" } to your root level build.gradle file

allprojects {
    repositories {
        jcenter()
        maven {
            url "https://maven.google.com"
        }
    }
}

Play services and Firebase dependencies are now available via maven.google.com with the release of version 11.2.0 of Google Play services and Firebase.

You can find the Google Play Services official doc here and the firebase doc here..

allprojects {
    repositories {
        jcenter()
        maven { url 'https://maven.google.com' }
    }
}

If you are using the android gradle plugin 3.x you can also use:

allprojects {
    repositories {
        jcenter()
        google()
    }
}

I just fixed same error by adding firebase-core dependency.

implementation 'com.google.firebase:firebase-core:16.0.1'