I've been playing with this module for a little while but cannot figure out why it isn't applying product discounts.

For my test case I'd like to discount the product "PC Watchdog" by £5 when 10-24 are purchased. The discount should be applied when the product is added to the cart.

Whatever settings I use, nothing seems to change. I've attached screenshots of my settings, am I missing something simple? (I'm using PHP 5 btw)