The business that works like ponzi.
That's a scam scheme. Even if you justify it that it's just "like" a ponzi and works like that then there's the obvious that it is.
Referral schemes where old users get paid through new users sign up
Typical pyramid scheme where the older people will earn from people signing up and paying for whatever fee is being required on. There's no other way on this scheme but to refer people and have them pay the signing up fee. That business model won't stay for so long thus, it's considered as a scam. If no new members and money comes, that's how the pyramid will collapse.