Yes, but you are responsible for complying with Facebook’s policy and Friendbuy reserves the right to close your account if you violate their policy.
Here’s a breakdown of what you can/cannot do:
You cannot incentivize a user to share just for the sake of sharing (i.e. share my company and you will get a discount.)
Any incentive offered to a user must be tied to their friend's activity (i.e. their friend registers, buys something, downloads an app, etc.)
From Facebook's Platform Policy Section 4.5: "Only incentivize a person to log into your app, enter a promotion on your app’s Page, or check-in at a place. Don’t incentivize other actions."
Review Facebook's Policy here: Facebook Policy Section 4.5