1. Go to Accounts module
2. Select the option of Invoice Details from Menu
3. Click on Search button and search for the invoice in which discount to be given
4. After searching for it click on Edit button so that invoice form will be editable
5. Scroll down till product table appears
6. Scroll the product table in the extreme right, there will be an option of "#Flat Discount"
7. A hash tag "#" means this option is editable
8. Click on flat discount option and enter the discount amount in it
9. Save the invoice details
10. When We print an invoice document, a discount amount will appear in the discount amount column in invoice pdf.