Hi sandi-radius,
That's a great question. I can see why you'd want to be able to apply credits from one area to the other for simplicity, but QuickBooks keeps these kinds of transactions strictly separate. This means customer transactions are handled independently from vendor transactions. Because of that, you'll need to settle things on the vendor side and then enter in the transactions you need on the customer side. I recommend speaking with an accountant to figure out the best way to do this. Our accountant users here in community should also be able to speak to this question and give you some guidance.
If you need an accountant, we can help you find one who's also familiar with QuickBooks Desktop. Check out our Find a ProAdvisor website and use your postal code to search for accountants in your area.
Here are a couple of articles about the transactions discussed here.
Enjoy the rest of your day.