credit coupons

We would simply like to be able to make reusable discount coupons in Drupal EC, Drupal 4.7, EC 3.x. At present this doesn't work and the patch described below also doesn't work for us, although we might have a database problem here.

Please don't tell us to upgrade as firstly coupons don't work in later version of Drupal or EC, second making a system that isn't backwards compatible is not a sensible software architecture decision and should be discouraged.

Thanks

Simon

See our notes below.

I am using drupal 4.7, with ecommerce 4.7 and a re-supplied coupon module

Got the basic site working, I need to be able to implement different types of incentives/discounts/extra charges.

Concept 1:

Charge standard price while checkout total is less than $150 (example).
If checkout total is more than $150 (say $250) then a discount is calculated as a percent of the difference (say 30%).
In this instance, Product value is $250, discount is $30, Discounted price is $220.
A registered user only to be able to see discount at the checkout screen.

Where would I need to modify the code to implement above?

Concept 2: