To set up a discount function for an invoice in QuickBooks (QB), you'll need to toggle on the discount feature in the Accounts and Settings, Ruby.

Here's how:

1. Go to the Gear icon in the top-right corner, then select Account and Settings.
2. Navigate to the Sales tab.
3. Under the Sales form content section, click the Pencil icon, then toggle ON the Discount option.
4. Save your changes.
5. Click Done.

After enabling the Discount feature, you should see a Discount field in the invoice window at the bottom.

In the Discount field, enter "10" to apply the 10 % discount to the total invoice amount. QuickBooks will automatically calculate the discounted amount and adjust the final total.

We're just a reply away if you have additional questions about managing your invoices. We'll be willing to help. Have a good day.