Thank you for providing the screenshot, @mac2it.
I can see that you're opening this report using QuickBooks Desktop Mac. Let me share some information about the negative transactions showing on the balance details of your vendor.
The negative amount listed along with the other transactions are payments applied to your bill transaction. This is how the payments are displayed if you go to the Vendor Center screen.
To ensure there are no over-payment or underpayments from a vendor, you can open the Vendor Summary Details and check the vendor balance from there. There shouldn't be any problems if you don't see any negative amounts through this report. You can check this guide if you need assistance with opening reports in Mac: QBDT Mac Guide.
Let me know how it goes. I wanted to ensure you get all the help you need. Take care and have a good one.