what should I give as return URL in paypal here integration with in mobile app

[phannindra4]

I'm integrating paypal here in a iOS app that I'm developing. I have used paypal backend code and deployed it on heroku as suggested on the page. I'm unable to figure out what to give for APP_REDIRECT_URL config var.

And also what is the difference between redirect URI, refresh URL and return URL.

Thanks in advance.