Since January 1st 2018, only those who have officially registered may work as sex workers. Since then, you have to expect a fine of up to 1000€ if you work unregistered. The so called “Hurenpass” is valid for everyone under 21 years for one year, and for everyone older than 21 years it is valid for two years. There is a lot of opposition and resistance from sex workers against the new law. FAU Berlin informs here about the new Prostitution Protection Act (ProstSchG) and the registration for sex workers.
Information on the Prostituiertenschutzgesetz Registration System for Sex Workers