How can I modify an invoice with a lower amount than previously sent out?

Good day, leonardo1.

We can open the invoice so we can edit it. Then, you'll want to send another copy to your client so they'll be notified. You can follow these steps:

1. Go to the Sales tab and select Customers.
2. Select the customer's name. Find the invoice you sent and select it.
3. Make the necessary changes. Click Save and send.

I have an article here if you need help in recording invoice payments in QuickBooks Online.

Keep in posting if you need anything else. Have a great day!