in the eCart object, you have set the discount calculation as:
"Based on Cart Subtotal"
subtotal of cart "minus" $_SESSION['PromoAmount']
if you enter "coupon10" this sets the PromoAmount at 10,
so you are telling the cart:
set the total of the discount to subtract from the cart at "<subtotal> - 10"
if you only have a 10 products in the cart, it means:
10 - 10
which equals a discount of $0.
if the cart subtotal is 70:
70 - 10 = 60
the discount becomes $60
instead of "Based on Cart Subtotal", use a flat rate discount of "$_SESSION['PromoAmount']"
the reason you ran into the problem on following the tutorial is that you are using a different type of discount, yours is a flat rate discount, the example in the tutorial is for a percentage based discount.
the tutorial is doing a 10% discount (subtotal * 0.10), whereas you are doing a flat rate of£10 or £20
