[SL] help with "credit"

[Myk R. <myk...@gm...>]

I need a little help understanding how to use part of the "credit" system. I 
have a customer who overpaid because I didn't have enough change on hand. He 
wanted to just have the excess added to his account. Now, when I go to do an 
invoice, it shows remaining credit. How do I apply this credit to a new bill? 
What should have been the proper way to log the excess payment in the first 
place?

Thanks,
-myk robinson