.NET for Android error XA0129
This issue happens when you are trying to use fast deployment on a device which
does not support it. In this case both the normal and backup types of fast
deployment failed. The Fast Deployment system makes use of the
run-as
feature of the Android OS. This feature was either not available or had
limited capabilities in API 20 and earlier
Disable Fast Deployment by setting EmbedAssembliesIntoApk = True
in your .csproj.
Or turn off Fast Deployment
in the IDE. You will still be able to debug on the device,
all the required files will be packaged inside the .apk.