I want to customize invoice want to add discount option

Hi @newtechsystems84,

Welcome to the Community. I can help you add a discount option to your invoices in QuickBooks.

There are two options you can try to apply discounts to your invoices. You can either include discounts per line item or directly to the total amount.

To enable item-wise discount or total discount:

1. Click the Gear icon and select Company Settings or Account and Settings.
2. In the left panel, select Sales.
3. Below Sales form content, enable the Item-wise discount or Total discount option. 
4. Click Save, then Done.

For more information, as well as how to show the Discount column in the printed invoice, I recommend the following article: Discount by line item on invoices and sales receipts.

Drop me a comment below if you have any other questions. I'll be happy to help you some more.