osDate 2.0 uses PayPal's Payment Data Transfer technology. However, to use this you must do following if you already have a PayPal account with IPN or PDT enabled:
a) Login to your paypal account.
b) Using account management functins, disable IPIN and PDT in the account. Also, remove any URL given for IPN or PDT.
c) In osDate's admin panel, provide the account details needed to access PayPal.
Ensure that the PayPal module is enabled, and that at least one permission level is defined that requires non-zero monetary payment.