I use PayPal's simple and well-documented IPN interface. You simply populate an HTML form with the details of the transaction; submitting it bounces the customer to PayPal's site (optionally themed to match your site design) where they complete the transaction before being bounced back to your site.

In the meantime, the PayPal software submits data to one of your own pages, where you process the data (including some simple validation to check that the customer paid the correct amount and that the PayPal data is trustworthy). Once done you can "activate" the service you are selling to the customer, which I usually do via an email (which could contain a link and password to a protected download site so they can download your software, or an activation key).

PayPal offer a free sandbox with which you can experiment with the API (setting up fake accounts to exchange funds), so it's pretty easy to work with.

You will (naturally) need to develop some sort of server-side web application to handle this, though. Of course, you could just set up a PayPal account and a hard-coded web form (they have wizards to generate said forms) and process the order manually when you receive an email from PayPal notifying you of a payment.

Quote:Original post by nebrad
Thanks this was very useful, but is this works only for USA? Because if I'm not in USA, can I also use PayPal?

Paypal also works in Europe, but not sure where else.

If you have more sophisticated needs, you may want to look at Kagi.