ENTERING BILLS IN A/P SYSTEM AND THERE IS NO SYSTEM CHECK AGAINST ENTERING DUPLICATE INVOICE NUMBERS?

Hi there, accounting-sunny.

Thank you for visiting the QuickBooks Community. I'll provide some details about setting up different features in QuickBooks. Then, ensure that you're able to receive a message if the said bill number is being used already.

There's a section in QuickBooks Online called the Advanced tab where you or your accountant initially set up your company file. From there, you'll be able to see the Warn me when I enter a bill number that’s already been used for that vendor option. With this, it could be the said feature is turned off and that is the reason why there's no system prompt against entering duplicate invoice/bill numbers. 

I suggest going to the Account and setting and you'll see the Advanced tab from that page. Then, make sure that the said mentioned option above is turned on. Please note that this prompt will only work with the same vendor and you can still create a duplicate bill number with a different vendor name.

Here's how:

1. Click the Gear icon at the upper right corner.
2. Choose Account and settings.
3. Go to the Advanced tab. Then, choose the Other preferences section.
4. Turn on the Warn me when I enter a bill number that’s already been used for that vendor option.
5. Click Save and Done.

For further details on how the Advanced account settings work in your QuickBooks account, you can open this article: How do I set my advanced account settings?.

I'm adding this article so you're able to view steps on how to run a specific report that will reflect all payments made to vendors: Run a report with vendor totals.

You can always post here if you still have concerns about settings in QuickBooks or other questions related to QBO. I'm here to help anytime. Take care and stay safe always.