Always good way to have first customers is bringing the people you know. The company that you knew personally. If they want to pay, the other people also will be. At beginning if the site is no popular just Google Ads or other payment commercial will help bring first customers.
first you need to know who are your users, then personally approach them and message them to try out your product. I would say start by doing invite only this way you will know that users are organically growing. I learned this from clubhouse and the idea behind it.
BAZO