Zero Cart Balance - PayPal Issue

[Guest]

I'm setting up a site using the PayPal module (only) to work with downloadable items. One of my items has a free demo that I would like osCommerce to handle as per the other products - i.e have a download link for the free item which is accessable within the 'My Account' area, as per the purchaseable items.

 

The problem I am having is that as it has a zero cost, if someone only 'purchases' this item and the cart total is zero, the payment system still goes to PayPal which fails it as PayPal will not process a zero balance.

 

Does anyone have any suggestions as to how I could achieve my objective?

 

Thanks!