Google CheckOut

From WHMCS Documentation

With Google Checkout, you MUST have an SSL Certificate installed on your server in order to use it. In addition to that, it must be fully valid or Google will refuse to perform the callback to the server.

Within the Google Control panel there is an integration section where you must enter the callback URL which WHMCS gives to you in the Setup > Payment Gateways page. It also gives you two options for the callback method - in WHMCS it is the XML Method that is used.

The option "For extra security, my company will only post digitally signed XML shopping trolleys. (Google should reject all others)" must be unchecked.

NB: The currency in Google Checkout must match the currency in WHMCS

Google Checkout Error

The Message

We encountered an error trying to access your server at https://www.yourdomain.com/whmcspath/modules/gateways/callback/googlecheckout.php -- the error we got is: javax.net.ssl.SSLHandshakeException: sun.security.validator.ValidatorException: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target

The Solution

This is going to actually be an issue with SSL certificate. Some times the gd_intermediate_bundle from the SSL authoritie gets corrupted and then you have to ask to have a rekey to reinstall the SSL. It can also be caused by not having the gd_intermediate_bundle installed at all, but just the certificate its self.