Cant get the uc_coupon to work with ubercart

Hi,
I just cant get the uc_coupon to work on my site.. I assign it both to individual users and Wholesale customers.. I then assign those users with a wholesale role that has the wholesale feature activated.. but when i buy a product nothing changes.. Im using paypal express checkout.. does that has something to do with it? Some detailed instructions for the module would be welcome,
thanks
eli