Why does online QB let me enter exact invoice info, same vendor, same invoice number twice ? Why doesn't QB tell me inv already entered -I do not want to pay twice?

Hello there, @lindak1119.

It's my pleasure to help you today so you'll be able to receive a notification or be warned if there's duplicate transactions/information created.

You may turn on a specific settings to be warned if duplicate check number and duplicate number is used. Let me show you how.

1. Go to the Gear icon.
2. Select Account and Settings under Your Company.
3. Go to the Advanced tab.
4. Click on Other preferences.
5. Put a check-mark on Warn if duplicate check number is used and Warn if duplicate bill number is used.
6. Click Save and click Done.

After turning it on, you'll be warned automatically if you've entered transactions with the same information. Don't hesitate to add a comment below if you have any other concerns, we're always here to help. Have a wonderful day!