Of the multiple methods for applying discounts at the invoice level, precedence is given in this priority sequence:
Priority 1) Quantity breaks and price breaks-> directly change the price of a line item.
Promo Price takes priority over Quantity Break
Priority 2) The discount button on the invoice screen is factored next. This will overwrite any promotionals and/or customer discounts.
Priority 3) Mix & Match takes precedence over Promo Pricing. If an inventory item is assigned to both Mix & Match and Promo Pricing, the price set for Mix & Match will be used on an invoice.
Priority 4) Whole store, department, category, and item promos-> Whichever one has the largest discount takes priority.
Priority 5) Customer Discount-> Even if a customer discount is greater than a promo it won't be factored if a promo exists.
Priority 6) Coupon-> A coupon will act as a line item. A coupon with a percentage discount will discount only the remaining price after all the other discount types are factored.
Mix & Match takes precedence over Promo Pricing. If an inventory item is assigned to both Mix & Match and Promo Pricing, the price set for Mix & Match will be used on an invoice.
In other words, discounted price will be overruled by a rule higher up the list,