Could anyone explain to me how does a paid Saas work please? I know for free Saas you can just create some kind of registration and authentication process which allows the users to use all features. But how does a paid Saas work? Sites like Shopify, Volusion, and many others offer different features at different prices ranging from free to a few hundred dollars. But how do they manage to do it? Btw, I've only had experience with general purpose e-commerce sites, so this kind of advanced things are confusing to me.