If you pay people to register under your ref link it works on games and rounds, also sometimes when people find new promos or giveaways they give their ref link and a non ref link, seems to be allowed aswell.

You are allowed to put your refferal link on your signature
So, when you make promotion, ask users to join through refferal link on your signature
And you might want to use link shortener, so every user can't know the refferal link

Any you should know it already when you join this forum