I am inputting supplier payments and a warning message appears saying that the payment reference number has already been used. Why is this happening?

Hi there, @usercelia-clark.

Allow me to inform you this is a system-designed feature where QuickBooks automatically assigns a check or reference number when paying bills. They all have an assigned number. It's our system's way of differentiating between each transaction.

To isolate the issue, you need to review the past vendor transactions and take note of their reference number. If the number still exists then you need to use the succeeding number for the checks you're going to record. For example, For example, the system will automatically assign the next bill as #2 if you change the preceding bill's number to #1.

Additionally, I'd like to leave this article to know more about adding a bill and recording payments towards bills: Enter bills and record bill payments in QuickBooks Online.

If you have more questions about recording transactions, please don't hesitate to use the reply button. I'm always around to help!