Why is it saying the invoice number is being used, when it hasn't?

Hi prestigedesignro,

The message/prompt you've received is due to the system detects that the invoice number for the specific has been used. QuickBooks has the option to warn you when entering/used duplicate invoice number.

Let's run an invoice list report to see the invoice numbers generated in your account.

1. Click on the Reports tab.
2. Click on Invoice List.
3. Select a Report period.
4. Click on Run report.

Then, check under No. column and double check if the invoice number you are trying to create is shown from the list.

If you wanted to turn off the settings to warn you duplicate invoice/bill number. Let's use the steps below.

1. Click on the Settings icon.
2. Click on Account & Settings.
3. Click on Advanced.
4. Click on Other Preferences.
5. Turn off Warn me when I enter a bill number that's already been used that.

Please know that I'm just a reply away if you need any further assistance managing invoices. Have a good one!