I found interesting point in In 4.0.0 BETA 3 release update: Added Hetzner referal link to get 20 euro of cloud credits
Is it working only for new Hetzner users?
Yes only works with created accounts from the link.
Oh snap! 
Yes this is for new accounts only, here it is again:
https://hetzner.cloud/?ref=U5z0aWoIB2Nj
Well just create a new account