a coupon (unique code) for a like clicked. what is the best way

Question

The unique code is given to whoever clicked like (only the first time he clicks) in order to make sure that he is not going to have a unique code again. I have to have his fb id in my database, but I read that it is impossible to know the fb id of someone who clicks like. Is there a solution?

If the like button will be on my fun page, is it possible then? I have already all the process of generating the unique code, and checking in my db if the code was used or know, I only have to keep in my db also the fb id to make sure he will not get more then once.

Answer 1

1. Create fangate (differentiate likers non-likers).
2. Is is_liker get user id with basic permissions.
3. On return after accepting the permission request check if user already got code.
4. If user never got code give him. Else display error message.