Joomla, 2Checkout and Acajoom Integration Plugin

I have an existing plugin in Joomla where a 2CO purchase button takes a user to 2Checkout to pay after they have entered their name and email address. Upon successful purchase they must be subscribed to the acajoom newsletter(s) specified by the instance of the plugin. I use Joomla 1.0.x. The acajoom subscription does not work. When the user makes a successful purchase on 2Checkout, the user is not subscribed to the newsletters I have specified. I want that fixed. I'll supply the source code of the current plugin.