Hi there, brittanynaturalf.

Thanks for checking in with us. I'm here to help you fix duplicate invoice numbers in QuickBooks Online (QBO).

If it's a duplicate invoice, you'll need to delete it. However, if it's only the invoice number that has duplicate, you have the option to edit the invoice number.

Here's how:

1. Open the invoice.
2. Scroll down at the bottom and click More.
3. Choose Delete if its a duplicate invoice.
4. Edit the Invoice no. if its only a duplicate invoice number.
5. Click Save.

Let's first locate the duplicate invoice number in QBO. Let me guide you how to get there:

1. Select Sales from the left menu.
2. Select the No. column to sort it.
3. When the Sales populate, it toggles the numbers in ascending and descending order.
4. Check for duplicates.

Here's an article to learn more about the different ways on finding duplicate invoice in QBO: How to find duplicate invoice and other transactions.

To prevent duplicate invoice number in the future, we can customize your Accounts and Settings preference.

Here's how:

1. Click the QuickBooks Gear icon.
2. Select Account and Settings.
3. Click the Sales tab.
4. Click the Sales form content section.
5. Uncheck the Custom transaction numbers box.
6. Click Save, then Done.

There you have it. Always feel free to drop by again anytime you need help. You have a wonderful day.