How do i register the earned discount?

Thank you for posting here in the Community, @i-abdulkarim.

Let me lend a hand so you can register discounts in QuickBooks Online.

The Discount feature allows you to provide discounts to your customers using an invoice or sales receipt. Before you start, you'll need to enable the option first from the Account and Settings section.

Here's how:

1. Go to the Gear icon.
2. Under Your Company, choose Accounts and Settings.
3. Select Sales.
4. Click Sales form content.
5. Put a check for the Discount option to turn it on.
6. Click on Save and then Done.

Once done, a field for the discount will now be available on your sales transactions (see sample screenshot below).

I've also included an article in case you need some ideas about adding a discount as an item (scroll down to Add a discount item with a fixed price): Add a discount to an invoice or sales receipt in QuickBooks Online.

Please know that I'm just a post away if you have any other questions. Have a great day ahead.