Ok so.... yesterday somebody messaged me to ask if I combine postage.  I replied that I did. 

Then I thought that person was going to bid on two things, but they only bid on one thing a few hours later.  They won the bid and I sent them the invoice.

Now today the same person bid on another item and they will win it in about 50 mins or so.  Postage will remain the same.

Seeing that I already sent them one invoice for the first item, what do I do?

Do I tell them to disregard the first invoice, and send them a new invoice for the 2 items?

This is the first time it's happened to me, so I'm a tad confused. Please help - cheers.  :8}