I am going to add facebook_audience_network flutter plugin with the following command.

flutter pub add facebook_audience_network

I am planning to add banner ad to details screen; after installing facebook ad plugin to my flutter app now I can import its code my details screen like below.

import 'package:facebook_audience_network/facebook_audience_network.dart';

To serve ads I need to create StatefulWidget. You will have to change the placementID. Just add your PlacementID after # sign.

class Details extends StatefulWidget {
 
  @override
  _DetailsState createState() => _DetailsState();
}

class _DetailsState extends State<Details> {
  


  Widget _currentAd = SizedBox(
    width: 0.0,
    height: 0.0,
  );

  @override
  void initState() {

    FacebookAudienceNetwork.init(

    );
    super.initState();
    setState(() {
      _currentAd = FacebookBannerAd(
        placementId: "IMG_16_9_LINK#YOUR_BANNER_ID",
        bannerSize: BannerSize.STANDARD,
        listener: (result, value) {
          print("Banner Ad: $result -->  $value");
        },
      );
    });
  }


 @override
  Widget build(BuildContext context) {
    return SafeArea(
        child:  Container(
                  margin: EdgeInsets.only(top: 5.0, bottom: 5.0),
                  child: _currentAd,
                 ),
	), 
}