on the fire exinguishers page, in the add to cart button, the discountPercentage column is set to gt it;s value from the cart:
$ATC_itemdiscountPercentage = "".$eCart1->DisplayInfo("discountPercentage") ."";// column binding
this is circular logic, it cant get the value from the cart, the add to cart is trying to add the value to the cart.
this should be set to the desired percentage instead, for example, 20%:
$ATC_itemdiscountPercentage = "0.2";// column binding