Yes.All the websites that offer free spin bonuses to win real cash prizes do so after you have a registered an account on their platform. They do so not only because theywant you to register and try their services, but also because they need to make sure you are legally allowed to gamble online.
All in all, there are free slots that pay real money, but you will have to be playing at real money online casinos as opposed to social casinos on slot apps, or playing titles in demo mode.