User Referral System using PHP and MySQL

Question

I already have a fully pledged membership system and want to integrate my own user referral system but want some tips, advice really on doing it.

My current registe

Answer 1

I found one query on that as I am making the same module. If the referral link is sent to another person who was not referred by the user, then what will you suggest:

(1) Either allow that person to register and pay to the user (As that can bring more users to site.) (2) Allow that person to register , but don't pay.