Here's how it works:
1) You create a initial regular PayPal invoice.
2) At any time you can create a new associated invoice connected to the initial invoice in step 1. This lets you bill additional fees, WITHOUT having to get it authorized at the time by a user.
Here's how we're using it:
We have a hosted version of GoTryTHIS with a recurring subscription, where we provide link cloaking and analytics on all the marketing you do to get people to your sites or affiliate promotions etc.
We crunch all the data and store it, for which there is real cost on our side.
Our monthly fee comes with 200,000 clicks each month. When you go over, we bill $0.00004 per click, rounded down to the nearest dollar. (That's 100,000 clicks for $4.) Now we can take PayPal and use an associated bill to add on the overage fee, where before we could not.
This means you now can do cellphone style billing with PayPal, charging per use. The approval process was pretty painless. They just needed to know exactly how we were going to use it. I'm sure you can come up with lots of ways to add this into subscription sites to increase your revenue and make sure costs are covered for extra service.
BTW, when you go to set this up, find yourself an account manager at PayPal. Makes everything go much smoother!
John Reel: My life as I hardly remember it.