android studio 3.4.1 and google admob change

In build.gradle (Module:app) change
...
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
        }
    }
...
dependencies {

   implementation 'com.android.support:appcompat-v7:28.0.0'
    implementation 'com.android.support.constraint:constraint-layout:1.1.3'
    implementation 'com.google.android.gms:play-services-ads:17.2.1'

In AndroidManifest.xml add

<manifest>
    <application>
        ...
        <meta-data
            android:name="com.google.android.gms.ads.AD_MANAGER_APP"
            android:value="true"/>
    </application>
</manifest>