Google Checkout

Requirements:

Configure Secure Pages:
Once your SSL certificate is set up and your web site responds correctly to https:// requests, Secure Pages must be configured to secure the communication between Ubercart and Google Checkout's servers. On the Secure Pages settings page, set "Pages which will be secure" to "Make secure only the listed pages". In the following field, put the following:

admin/*
google_checkout

More entries such as "node/*/edit" and "user/*" may be added if desired. SSL sacrifices performance for security, so make sure to secure only what needs to be. To prevent errors on autocomplete fields, add "*/autocomplete/*" to the "Ignored pages" field.

Configure Google Checkout:
The Google Checkout settings page is found under Store administration > Configuration. A Merchant ID and Merchant Key are needed to send orders to Google Checkout, and they can be found through the link to the Merchant Center at the top of the page. At the Merchant Center, go to the Settings tab and click on Integration. The Merchant ID and Key (which should be mailed to you during registration) appear on the right-hand side.

UC Google Checkout is designed to provide digitally signed carts, so check the first box. The callback URL is also found on the settings page, but it follows the pattern of https://www.example.com/google_checkout. (Note: I have not been able to use https for the callback in test mode. If you have trouble getting checkout notifications in Ubercart, remove the "s" in the callback, and unsecure the "google_checkout" path in the Secure Pages settings.) The callback method is XML.

It is recommended that all the Advanced Settings are turned on, though none of them appear to be crucial.

Enabling UC Google Checkout creates a new cart pane that holds the Google Checkout button. This pane may be disabled to turn off Google Checkout processing, but it should be kept as close as possible to Ubercart's checkout button. If any products in the catalog do not conform to Google's purchasing policies, a checkbox is added to the node edit form which prevents it from being purchased through Google Checkout. Carefully read Google Checkout's user documentation and follow all applicable policies and regulations.