Spain is a bit of a different duck in the water. Simular as Portugal prostitution is'nt forbidden, but pimping or making money off a transaction in between a client and sexworker as a third party is prohibited by law. This means that girls generally could work independent or join the few legal brothels, however there are different approaches to working in brothels in Spain. What is important to know is that a owner cant make money off of girls.
Often a fee is paid upon hiring or renting of a room inside a brothel. Usually girls that choose to work as escort often join large websites and it is possible to pay a fee for listing on these websites that advertise independent escort girls. In Spain it's a almost as simular situation as with Portugal. If you plan to head to spain to work in prostitution be aware of lots of traffiking which is a dangerous trend at this very moment.
Trafficking means that girls or workers are usually arranged for their arrival in Spain under either false conditions or simply put to work and leave 50% or even more of their earned money to their managers. Note that this is illegal by law and we recommend you not to accept any of these conditions. Spain is also the country often used for Human Trafficking due to it's easy visum integration. This makes it a too easy proces for acces to europe.