Hi there, and welcome to Wattpad! In order to have a paywall on your stories, you need to either apply for the Creators Program, which grants you access to special pitching rights, or to see if the recent pitching contest is still open to the public. These options can take a lot of hard work and time though, as you prepare a pitch and submit it for judging. If they like it, they’ll reach out. Keep in mind that revenue isn’t guaranteed though — it depends on how well your stories do after the fact. So if you love writing, I highly recommend giving it a go, but if you’re looking for a quick and reliable way to make money, you might want to consider other options!
I hope that helps and you enjoy your stay :)