Is there an alert for when you are inputting expenses and you put in a duplicate invoice number?

Hi there, 

QuickBooks Online allows you to track your income and expenses using invoice numbers, bill numbers and cheque numbers. It's essential that these numbers are only used once for the accuracy of your records. I'd be happy to share more information about how QuickBooks can warn you of duplicates. 

There's two warnings you can set up in QuickBooks Online:

• Warn if duplicate cheque number is used
• Warn if duplicate bill number is used

To turn on those settings, click the Gear icon > Account and Settings > Advanced > Other preferences. Toggle these settings to On. 

At this time, the system doesn't warn you if duplicate invoice numbers are used. You're able to use custom invoice numbers if that helps you keep better track. To turn on custom invoice numbers, click the Gear  icon > Account and Settings > Sales > toggle on Custom transaction numbers. 

I think adding a warning for duplicate invoice numbers would be a great addition to the product. I'd be happy to pass along your feedback about this to our product development team. We're here to help make the products even better!

If you have any other questions, let me know. 

Have a great day.