Hi there, @Angie13,

A negative balance on your vendors account can happen when payable checks were written, but there are no bills created or the original bills got deleted. It's also possible the bill was overpaid. 

Let's pull up the Accounts Payable Aging Detail report and scan through the report to see negative amounts.

Here's how:

1. Go to the Reports menu.
2. Select Vendors & Payables, then A/P Aging Detail report.
3. Locate the negative amount under in line with the vendor. 
4. Open the check to see if there are bills paid in this transaction.
5. If no bills located here, then you can create a bill against the check. 
6. Make sure to enter the same amount, then pay the bill.

Once done, go back to the Vendor list, the balance will is now zero.

On the other hand, if the bill was overpaid, you have the option to apply the credit to the next transaction.

Should you need some clarifications, please let me know and I'll get back to you.