How did I get duplicate invoice numbers?

I can think of a reason why an invoice is duplicated. @lance24.

Let me share some knowledge and tips on handling it in QuickBooks Online.

An invoice number becomes a duplicate when it is reused. Although it's possible, QuickBooks will warn you if you use the same invoice number twice. See the screenshot below for reference:

The Custom transaction numbers feature is most likely enabled, allowing you to enter the same number accidentally. It's also possible that the Yes option is selected when creating a duplicate invoice. I recommend reviewing the invoices to verify if those are two different valid transactions. If so, you can manually change the invoice no. of one of the invoices. Here's how:

1. Open the Customers & leads menu.
2. Locate and select the customer to whom the invoices are sent.
3. From the upper right part, enter your desired digits in the Invoice no. box.

If the issue continues, I suggest performing some basic troubleshooting procedures to make sure you're not experiencing a browser-related problem. Start by logging in using an incognito page. Here are the shortcut keys to open it:

• For Firefox or Microsoft Edge, press Ctrl + Shift + P.
• For Chrome, press Ctrl + Shift + N.
• For Safari, hold down Command + Shift + N.

If this works, you must clear your regular browser cache. This prevents unusual browser behavior. 

If the issue continues, use another supported browser.

Lastly, if this happens to be a recurring invoice, kindly let us know by replying to this thread.

Once you're good on your end, read these additional modules about personalizing invoices and handling customer payments:

• Customize invoices, estimates, and sales receipts in QuickBooks Online
• Record invoice payments in QuickBooks Online

You can always get back to us. The Community is available 24/7 to answer further questions about invoices and QuickBooks. Keep safe.