Having consistent error trying to use AdMob in Xamarin.Forms App

Hi,

I have been trying to put banner ads in a couple of my Xamarin.Forms aps. I followed the video on James Montemagno on Channel9
https://channel9.msdn.com/Shows/XamarinShow/Episode-26-Monetizing-Mobile-Apps-with-Ads
and also used the blog post at
https://montemagno.com/xamarinforms-google-admob-ads-in-android/

I get everything installed and all classes added as per the examples. I am having a problem with the AndroidManifest.xml file. The eroor I get is:
No resource identifier found for attribute 'configchanges' in package 'android' DewPoint.Android

This is what I have in my AndroidManifest.xml file

Can someone help me find a solution. Or is there a more recent example somewhere ??

Thanks in advance