Plugin with id 'com.google.gms.google-services' not found

Question

I have followed this link to integrate ads in my app. But it shows this error:

This is

Answer 1

simply add "classpath 'com.google.gms:google-services:3.0.0'" to android/build.gradle to look like this

buildscript {
    repositories {
        maven {
            url "https://maven.google.com"
        }
        jcenter()
    }
    dependencies {
        classpath 'com.android.tools.build:gradle:3.0.1'
        classpath 'com.google.gms:google-services:3.0.0'

       // NOTE: Do not place your application dependencies here; they belong
       // in the individual module build.gradle files

    }
}

and also add "apply plugin: 'com.google.gms.google-services'" to the end of file in android/app/build.gradle to look like this

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