How to implement paypal in facebook application canvas using PHP?

I want the user to sub开发者_StackOverflow中文版scribe my app in two ways means there are two choices say 200$ and 350$ subscription are available. Firstly I want to direct them to Paypal inside the canvas and then return to the app's page.I want to use PHP libraries ..

Could you just implement PayPal as you would any other PHP application, and then specify the return_url parameter when your form's posted to PayPal as your Facebook app's URL?