I find that Brad doesn't explain things very well sometimes.
- Go to http://www.livejournal.com/invite/gen.bml and make sure you've generated all the codes you're entitled to.
- Make sure the e-mail address for your LJ is set to the one you want to receive the coupon in.
- Go to http://www.livejournal.com/invite/claim.bml to get LJ to e-mail you a coupon code (it looks a bit like an Invite Code, but there's a dash in it).
- Go to http://www.livejournal.com/pay/. In the "Add to Order..." section, select the service/user you want to buy, click "Add to order". In the "Have a coupon?" section, enter the coupon code that LJ e-mailed to you.
Add all the services and people in this one session. You have to use up the entire value of the coupon in one transaction or the credit will be lost. To use up the maximum value of the coupon, you have to buy enough for the exact amount or in an amount over it and pay the extra.