Is there an alert in QBO to warn of duplicate invoice numbers when entering bills?

I've got you covered, @lindab2810.

QuickBooks has the option to warn you when entering a duplicate bill number. You'll want to make sure that the feature is turned on. Here's how:

1. Sign in to your QuickBooks Online (QBO) account.
2. Click the Gear icon, then select Account and Settings.
3. Select Advanced from the left menu.
4. Go to the Other preferences section.
5. Then, turn on the Warn me when I enter a bill number that’s already been used for that vendor option.
6. Click Save, then Done.

After turning on the option, you'll now get a prompt that the bill number you're entering is a duplicate.

As always, you can visit our QuickBooks Community help website if you need tips and related articles in the future. 

Please know that I'm just a reply away if you need any further assistance managing your bills or vendor transactions. Have a good one!

Hi, lindab2810

Move to the right top and click the Gear icon > YOUR COMPANY > Account and Settings > Advanced > Other preferences > turn on the button to Warn me when I enter a bill number that’s already been used for that vendor.

Feel free to contact me for any clarifications.