On the integration settings at the Google Checkout Account I notice today that we are using API VERSION 2.1.
We've using Google Checkout with Zen Cart for a long time, with no problem.
Today, 08/11/2010 after upgrading our Zen Cart to 1.39e I revisited the Google Integration settings and notice that they have added a drop down box to select the API Version to use, and they post:
"If you are using a third-party shopping cart, please consult your shopping cart provider on which API version to use. If you are unable to confirm which version to use with your shopping cart provider, using Version 2.0 is safest. "

Should we upgrade to Google API Version 2.5 which is the most current one?