No, Upwork will only charge you if you make a request. But yes, there is such a thing as Upwork Plus Membership and once you register, it automatically renews itself every month. But it is very simple and in your hands to switch back to Basic Membership. Plus, you don't go back to basic membership immediately when you stop your plus membership. The amount you pay is monthly and you will return to basic after the month ends. And again, if you return the basic membership once, they won't receive the second payment.