By default, a discount field is not displayed on an invoice page. If you want to give your customer a discount, you can do so while creating the invoice. If the invoice has already been prepared you can edit this to apply a discount.
To add a discount, open the invoice, go to the Actions button and select Edit to put this in edit mode. If you are creating a new invoice, you will already be in edit mode so you need not click on the Edit button.
Select Add Discount from the Actions tab drop-down menu.
On the Set Discount window, enter the value of the discount. Indicate if the entered value is a dollar amount or a percentage discount. Select from the drop-down and Save the discount.
The Discount field will be added to the invoice.
Click the Save button to apply the changes. The invoice will remain open and you can continue working on it. To save and exit the invoice, click the Save and Close button.
The discounted value will be displayed on the Invoices list.