Neither method (New-> Receive Pmts OR Invoice->Receive Pmts) works for me to apply a credit to an invoice. 

I created the credit last week and it's in the customer's transactions, but does not show in receive payment.

FYI - The credited amount is not the same as the new invoice I want to apply it to so it doesn't show.

So... how do I apply a credit to an invoice when it's not the exact amount of the invoice I want apply it to?