OK - not completely there yet but it did strike me that I just need to launch an app.
So, to that end I connected my phone to my PC adn ran the Android device monitor.
LAunched Google Pay on my phone and sorted through the wheat and chaff to find the package name which currently is 'com.google.android.apps.walletnfcrel'.
A little more googling and I found a way to test if the app is installed......
private bool isAppInstalled(String packageName)
{
var context = Android.App.Application.Context;
var pm = context.PackageManager;
bool installed = false;
try
{
pm.GetPackageInfo(packageName, Android.Content.PM.PackageInfoFlags.Activities);
installed = true;
}
catch (Exception e)
{
installed = false;
}
return installed;
}
...and then if it is installed I can fire it up as follows.....
var googlePayPackageNAme = "com.google.android.apps.walletnfcrel";
var context = Android.App.Application.Context;
Intent gpIntent = context.PackageManager.GetLaunchIntentForPackage(googlePayPackageNAme);
context.StartActivity(gpIntent);
For now I am happy with that.....other things to do but I will try at a later date to actually trigger the add payment method process.
Thanks to other postings on SO.
Hope this helps others.