this depends on how you are managing the price.
Are you setting the item price using a calculation?
Normally, I would create a calculation named realPrice to calculate the price total
then modify the TotalPrice calculation. in the total price calculation, replace:
[Price]
with:
(realPrice calculation code)
then in the code that paces the item price to paypal:
$PP_DirectPayment_itemized[1][$nextIndex] = "".$eCart1->DisplayInfo("Price") ."";
use the realPrice instead:
$PP_DirectPayment_itemized[1][$nextIndex] = "".$eCart1->DisplayInfo("realPrice") ."";