Even after completing the wagering, casinos won't let you just take the money and run. If you got your free spins without a deposit, you need to confirm a banking method for the withdrawal.
In practice, you need to make a deposit and play through the deposit sum at least once. Only then you can withdraw your remaining deposit and the free spin winnings.
This may seem unfair, but it's a legal requirement and part of casinos' anti-money laundering practices. However, it's also a way for casinos to discourage bonus abuse.