If the line discount is use for multiple customers, you can setup Customer Discount Group then assign the group to the customer card.
It will be easy to maintain the line discount by use Customer Discount Group
Create Customer Discount Group
1 - Go to customer discount group
2 - Enter the Code for the discount group (e.g. HKTVM) and the Description
3 - Select Navigate => Sales Lines Discounts
4 - Setup Sales Line Discount
(1) - Sales Type and Sales Code default by system
(2) - select Type = Item and Code= select item from item card
NOTE: System will default base unit for Unit of Measure Code.
If the customer group buys the item use different unit, user need to change the sales unit and the unit must create in Item Unit of Measure of the item card.
(3) - Enter Line Discount %