When we get an email notification that a user bought a premium package, I add the information to the DB. Disadvantage: Lots of work, and user can use premium service only after i entered the data which might take a few days.
we let the notifications to be send to a separate email account, you write a program that checks emails every couple of minute, parses the emails and adjusts the settings in the DB
we use the API of PayPal to trigger a script on our server that adjusts the DB
backend for #114
I see different options