The discount you give to a product with a list price of zero is based on the price you enter on the order row.
Each time you change the price, the new price becomes the base for the discount and the discount on that row is reset to zero.
Here's how it works:
- Add a new product to your order with a price of zero and:
- Set the price to €100
- Set the discount to 50%
- The price of the product is now set to €50
- Save the order
- Open the order again and:
- Increase the product price to €200. The discount is reset to zero.
- Set the discount to 50% again
- The product price is then €100 because the discount is based on the new price (€200)