Please use the following package for your admob function. This is implemented and maintained by google.dev team

google_mobile_ads: ^0.13.0

Version can be changed over the time. Please check the link for newest version.

Android configuration

<manifest>
    <application>
        <!-- Mention your app id here -->
        <meta-data
            android:name="com.google.android.gms.ads.APPLICATION_ID"
            android:value="Your_app_id_here"/>
    </application>
</manifest>

iOS configuration

Goto ios/Runner/Info.plist file and add two keys: as below

<key>GADApplicationIdentifier</key>
<string>ca-app-pub-3940256099942544~1458002511</string>
<key>SKAdNetworkItems</key>
  <array>
    <dict>
      <key>SKAdNetworkIdentifier</key>
      <string>cstr6suwn9.skadnetwork</string>
    </dict>
  </array>

You can check more about the key file here.

Initialize the admob in flutter app

void main() {
  WidgetsFlutterBinding.ensureInitialized();
  MobileAds.instance.initialize();

  runApp(MainPage());
}

I will udate this page, when i get sometime, how to create banner or other ad types.

Thanks