I can certainly help you, @anjum.

You can create a discount item with a customized name in QuickBooks Online. This way, you can add or apply it as a line item on your invoice transaction. Before that, make sure your Discount feature is activated to easily track any discounts you give to customers.

Here’s how:

1. Go to the Gear icon, then choose Account and Settings.
2. Select the Sales tab.
3. In the Sales form content section, click the Pencil icon.
4. Turn on the Discount setting.
5. Press Save and then Done.
   

Then, follow the outlined steps below to create an item.

1. Select the Gear icon, then choose Products and Services.
2. Press New.                      
3. Select Non-inventory or Service for the type.
4. Enter the custom name in the Name field.
5. In the Sales price/rate field, enter the discount as a negative amount.
6. From the Income account dropdown, you can select the Discounts given account that QuickBooks created when you turn on the discount setting.
7. Select an appropriate tax rate so that the discount is nontaxable.
8. Click Save and close.
   

Once done, you can now apply the discount item to your sales form. I’m glad to show you the steps.

1. Select the + New button, then choose Invoice.
2. Add your products or services in the Product/Service column.
3. Select the discount item you just created. Make sure it's a negative amount.
4. Fill out the rest of the form, then hit Save and close.
   

You can read this article to learn more about the discount feature: Add a discount to an invoice or sales receipt in QuickBooks Online.

Also, if you need to customise the appearance of your sales forms, just refer to this reference for complete instructions: Customise invoices, estimates, and sales receipts in QuickBooks Online.

Please don’t hesitate to comment below if you have any other concerns or questions about managing your transactions. The Community is always here to provide you assistance. Take care!