[GNC] Split Payments?

[Eric H. Bowen]

I'm fairly new to using the Accounts Payable function. I have a vendor 
which is owed two invoices, one larger one which she has agreed to 
accept four monthly payments on plus one smaller invoice which I wanted 
to pay up front right now. I made a payment for 1/4*A + B, but when I 
attempted to "assign as payment" it only applied it to a portion of the 
larger invoice A. What's the proper technique for dealing with this kind 
of situation going forward?