Oi
Estava configurando o FCM na minha aplicação, e na hora de sincronizar o gradle, recebi o seguinte problema:
Error:(39, 0) Version: 8.4.0 is lower than the minimum version (9.0.0) required for google-services plugin.Aqui está todo meu build.gradle:
apply plugin: 'com.android.application'
android {
    compileSdkVersion 23
    buildToolsVersion '26.0.2'
    defaultConfig {
        applicationId "br.com.alura.agenda"
        minSdkVersion 15
        targetSdkVersion 23
        versionCode 1
        versionName "1.0"
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
    }
    productFlavors {
    }
    packagingOptions {
        exclude 'META-INF/LICENSE'
    }
}
dependencies {
    implementation fileTree(include: ['*.jar'], dir: 'libs')
    implementation 'com.android.support:appcompat-v7:23.3.0'
    implementation 'com.android.support:cardview-v7:23.3.0'
    implementation 'com.android.support:support-v4:23.3.0'
    implementation 'com.google.android.gms:play-services:8.4.0'
    api 'com.squareup.retrofit2:retrofit:2.3.0'
    api 'com.squareup.retrofit2:converter-jackson:2.3.0'
    api 'com.squareup.okhttp3:logging-interceptor:3.9.0'
    implementation 'com.google.firebase:firebase-messaging:11.0.4'
}
apply plugin: 'com.google.gms.google-services'Alguma solução? Obrigado!
 
            