what's the invite system in HT

i want to know what is the invite system in HT(HeavenTracker)
i am pu there but didn't recive any invite
i remmber the one who invite me...he is not pu
any one can help ?

if you are PU u get 4 invitations every 28 days, if you donate and the nuber of your invitation is less the 4 they increase it to 6
There was once when all users class got 3 invitations.

i have downloaded 3 gb

they give me 3 inv

as I said, there was one situation when they gave all USEr class people 3 invitations

clear ur pms I want pm u