Hello,
First off, let me mention that I haven't worked with OsDate. However, I am very familiar with the PayPal API and Smarty (Do you happen to know what version you are using? Just curious). I have roughly 8 years experience with LAMP and can figure most CMS's out fairly quickly, so if you are unable to locate someone familiar with OsDate I can give you a hand.
Also, out of curiosity, why wouldn't we be able to test it in the PayPal sandbox instead of live accounts?
Thank you for your time & consideration,
Keith