How to apply a credit to a Vendor Account

SOLVED

Hi there, this is my first ever post, and I'm not that great with Sage 50, so please, bare with me!  And if I posted this in the wrong group, I apologize!

We received a bill that was 2 months worth of charges, so we assumed we missed a payment and paid the amount owing.  (Turns out, our previous payment was just late, so when the next invoice was issued, it showed 2 months owing, and not 1.)  We figured out the error, and contacted the vendor.  They quickly issued us a direct deposit payment to credit the account, but I have no idea how to apply this credit.  Can someone help?