Log into your PayPal account and sign-up for the "PayPal Sandbox" feature
under this area: PayPal Web Services & Developer Central
This allows you to experiment with transactions without actually making
a real transaction. Great for development.
You'll notice that once a person pays, you can have a "session" variable sent
back to any server-side script (such as PHP or Perl). That script can then
handle the variable and do whatever it needs to do.
I'm thinking you can find a free PHP/MySQL members area script and
customize it ... or utilize the features that PayPal offers.
People sort of "scoff" at PayPal, thinking it's not professional, but in reality,
it offers some great features that many don't use. It's just a matter of
looking into it and learning how to do some PHP programming.
There are so many free members area scripts:
Without searching each one, I'm guessing one of them has a means of utilizing
a "paying customer" variable ... or a variable coming back from a merchant
If I find a particular free script that interfaces with PayPal, I'll let you know.
Here's a paragraph from PayPal's SandBox:
Instant Payment Notification (IPN) is PayPal's interface for handling real-time purchase confirmation and server-to-server communications. IPN delivers immediate notification and confirmation of PayPal payments you receive and provides status and additional data on pending, cancelled, or failed transactions.
# Customize your website's response to customer purchases in real-time
# Track customers via IPN "pass through" variables
# Deliver access keys for software downloads and other digital goods
# Automate your fulfillment operations