Step 1: Discount can be added to any Invoice by Selecting the Edit Invoice option and choose the Add Item button and select the Option other as shown below.

Step 2: Enter the Rate, Quantity and Discount Amount along with the Description as shown below.

Step 3: In the Invoice Preview click on the generate Files as shown below.

Step 4: Delete the older Invoice file and generate a new invoice and click on Submit button.

Step 5: The Discount Amount will be now debited from the Amount to dispaly the Invoice Amount as shown below.