Is it possible to make people like on Facebook to get coins for free?

I believe this is actually against the Apple terms of service now. You re not supposed to exchange currency for likes. Although this might only apply to ratings in the appstore.

You can use the Get object to call a facebook url, which will in turn open Safari. As a general rule, most apps simply check that the button was pressed and then grants the free thing. It is not based on an actual like button being pressed, just the user thinking they need to press the like button. Check a lot of games and you will see that if you just go back to the app without pressing like in facebook, you will have been granted the free thing.

As for requiring a legitimate facebook interaction, you would need access to the facebook api, which I believe is not supported by any official means. There might be a 3rd party extension (that you will need to pay for). But no easy way I know of without doing some fiddling in xcode.

I believe mobichan is right. I think your game would be rejected. I'd hate for you to do all that work for nothing.

What he is doing is fine. Nothing in the guidelines prevents this. I would however recommend the verbiage of "Do you like Classroom Jerk?" ... "Like Us on Facebook and keep up with new developments and we'll give you 20 free coins" etc. etc. Something more docile. I would also not make it a feature but rather something that shows up after X number of gameplay so it's not annoying or missed.

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Offering currency to download other apps however has been a problem.

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Its fine....you cant give free coins to rate you app on appstore....but no to like facebook page