Esse é o Erro no Sync
The library com.google.firebase:firebase-iid is being requested by various other libraries at [[16.0.0,16.0.0]], but resolves to 17.0.3. Disable the plugin and check your dependencies tree using ./gradlew :app:dependencies.
Minha build.gradle(Module:app)
dependencies {
implementation fileTree(include: ['*.jar'], dir: 'libs')
implementation 'com.android.support:design:27.1.1'
implementation 'com.android.support:support-v4:27.1.1'
implementation 'com.android.support:cardview-v7:27.1.1'
implementation 'com.android.support:appcompat-v7:27.1.1'
implementation 'com.android.support.constraint:constraint-layout:1.1.3'
testImplementation 'junit:junit:4.12'
androidTestImplementation 'com.android.support.test:runner:1.0.2'
androidTestImplementation 'com.android.support.test.espresso:espresso-core:3.0.2'
api 'com.squareup.retrofit2:retrofit:2.4.0'
api 'com.squareup.retrofit2:converter-jackson:2.4.0'
api 'com.squareup.okhttp3:logging-interceptor:3.11.0'
implementation 'com.google.firebase:firebase-ads:16.0.1'
implementation 'com.google.firebase:firebase-core:16.0.4'
implementation 'com.google.android.gms:play-services-maps:16.0.0'
implementation 'com.google.android.gms:play-services-ads:16.0.0'
implementation 'com.google.firebase:firebase-messaging:17.0.0:15.0.0'
}
apply plugin: 'com.google.gms.google-services'
E no Build.Gradle (Project) a dependecia
classpath 'com.google.gms:google-services:4.0.1'
Se alguém puder me ajudar, porque realmente não consigo encontrar a resposta em lugar algum.