Hi there, @roseochoa44,
QuickBooks Online allows you to use the Refund receipt feature to refund goods or services that don't satisfy the customer. You need this feature if you've already created and sent the invoice.
To do so, you need to create a check and pair it with the credit. Feel free to read through this article: Record a Customer Refund for detailed steps and additional information.
If you're still on the process of making the invoice, you can add a discount field to it. To start, you need to turn on this feature first so you can enter a discount percent or amount.
Once done, you can then follow the steps outlined below:
Step 1: Create a discount account.
Step 2: Create the discount item.
Step 3: Use the discount item on an invoice or sales receipt.
For the detailed steps, you can read through this link: Apply a discount on an Invoice or Sales Receipt. Then, scroll down and go to the Add the discount as an item section.
Let me know if there's anything else you need with your invoices and I'd be glad to help you out.