Utilizing the Ecommerce Templates shopping cart, if your Google payment integration doesn't seem to be working, login to your WCP and go to WebSite Settings > IIS Settings > Authentication and make sure Basic is NOT checked and that Integrated Windows Authentication is checked.

If that does not help, make sure you have the latest update from Ecommerce Templates as they released v6.1.3 which fixes some issues with the Google payments.

If that still does not help, please open a ticket and let us know the domain and mention we need to verify the Authentication settings for the /vsadmin/gcallback.asp file.