what?
edit: you don't need to add anything at all with shipping its over $50 and you can apply the coupon
edit edit: sorry, i didn't see your coupon problem. when i added it to my cart, it first added on the shipping cost and then when i put the coupon in, it took the $20 off. i haven't checked out, so it might bring that up error later on, but i copied and pasted this from my shopping cart:
SKU# ITEM QTY INVENTORY PRICE TOTAL
TWENTY
Remove $-20.00 $-20.00
601816 Supreme Mag Drive Pump Model 3 - 350 gph
Remove IN STOCK $44.99 $44.99
Sub Total $44.99
Shipping & Handling
Basic $7.99
Discount/Ship Credit -$20.00
Total $32.98