paypal.com/developer
developer.paypal.com
paypal.com/sdk
Setting up recurring payments is possible using PayPal subscriptions. A Premier or Business account is needed to use PayPal subscriptions. You can create daily, weekly, monthly, and yearly subscriptions. You can also create trial periods where the subscription is offered for free or at a reduced rate. For more details on using subscriptions, see the Subscriptions Guide (PDF, HTML).
Here's a sample subscribe button: (click it to send me money!)
Important Parameters:
business: the paypal email account the payments go to
item_name: the name of the subscription
item_number: use this as unique identifier for person subscribing (id)
a3: how much $ per subscription transfer
p3: length of billing cycle
t3: billing cycle unit
srt: how many cycles to bill (stop subscription after)
Instant Payment Notification (IPN) Stuff:
If you have Instant Payment Notifications activated, you will receive an IPN on: