When you're creating a bill (Purchases menu > Create bill), you can add a separate line to the bill for the discount.
Use the Description column to provide some details, and enter the discount as a negative amount. Allocate the discount to the applicable discounts taken account—this will likely be the same as the linked account you've set up for your supplier discounts (see above for details). Check with your accounting advisor if you're not sure which account to use.
Can I use an item with a negative value for supplier discounts?
No. You'll get an error if you try to use an item with a negative selling or buying price in a bill.
In older versions of MYOB Essentials, you could create an item with a negative price and use it to create discounts in bills.
To record a supplier discount on a bill in this version of MYOB, you can use the Discount (%) column (when you use the Services and items bill layout) or add a separate line with a negative figure in the Amount ($) column, as described above.