Retail Express orders are composed of individual products that can be sold for a unit price. TIMES a quantity. It does not have order level discounts or coupon codes that apply across the whole order.
So how do we apply these when the eCommerce system order has them or a special discount coupon is used? How do we make sure the GST is all correct too?
The answers is a VERY complex method to try to locate the discount and allocate it to line items AND the tax. The integration does have it’s own discounting engine that will discount the order when sending it into REX. Most importantly what you see on the website may not be what you see in REX.
For WooCommerce the GST calculation can be quite different from that calculated by Retail Express. For this reason we need to ignore the WooCommerce tax calculation and regenerate the tax inside Retail Express with its rules.
This can be very difficult to follow when there is a discount code that applies for certain products. For example if the order has 4 products and the discount is only for 1 it spreads it evenly across all products as it has no way of knowing about the "special" product,
For this reason coupons are best managed when they provide order level discounts which then we can pass through to what retail express can handle. If you provide item level discounts then the results in Retail Express may not be what you expect.