To add motivation to the referrers, increase the money received according to the number of players you've invited.
For the first player invited you get 100k
second - 120k
third - 140k
4th - 160k
5th - 180k
6th - 200k
7th - 220k
8th - 240k
9th - 270k
10th - 300k (max.)
11th - 300k
12th - 300k, etc.
Of course only once they get to level 100