Hi anonymous26!

QuickBooks Online won't allow you to save an invoice with a negative total. I'm here to help you.

What I can suggest is to record the overcharge using a credit memo so you can keep track of it. You can use the credits as a payment to your open invoices.

Follow these steps:

1. Go to the +New button and select Credit memo.
2. Select the Customer and other details required.
3. Tap Save and close.

Then, here's how to apply it to an invoice:

1. From the +New button, select Receive payment.
2. Select the Customer. In the Outstanding Transactions section, select the open invoice you want to apply the credit memo to.
3. In the Credits section, select the credit memos you want to apply. Then, enter how much of the credit you want to apply in the Payment column. Make sure the Amount Received is $0.
4. Leave the Payment method, Reference no, and Deposit to blank.
5. Tap Save and close.

You can apply the remaining credits to future invoices. You can check the detailed steps here: Create and apply credit memos or delayed credits in QuickBooks Online.

Additionally, you can find the different ways to handle overpayments on this link: Handle a customer credit or overpayment in QuickBooks Online.

For other income and customer concerns, you'll want to visit this page: Sales and customers.

Keep on posting here if you have other questions. We'll help you!