Is there a way to set up an alert for duplicate bill entry

There is, indeed, @northstarrefrige.

I'd be happy to walk you through the steps for receiving an alert for a duplicate bill entry.

Here's how:

1. Log in to your QuickBooks Online (QBO) account.
2. Navigate to the Gear icon and select Account and settings.
3. Select the Advanced menu.
4. Hover to the Other Preference section.
5. Select the Warn me when I enter a bill number that's already been used for that vendor. 
6. Click Save and then Done.

Once you're all set, you might want to check out this article to help you manage your bills more effectively: Enter bills and record bill payments in QuickBooks Online.

I'll be available if you require additional assistance with your bills and QBO. Please tag me in your response, and I'll get back to you as soon as possible. Have a safe and enjoyable day!