The cart contents are stored in a session variable. Session variables use a cookie to track the session contents. The cookie is set based on the domain.
When a user comes to your site at:
a cookie is set to track session contents, when they get redirected from paypal back to your site, they are directed to a different domain:
in the WA_Globals.php, make sure to set the $WAGLOBAL_Root_URL variable to www.voyagermoon.com/