Through webinar report page of Zoom web portal page, you can know the registrants who has filled inputs and submitted, but not paid like the pic below.
Welcome to the Developer Forum @shinseikaikanoffice! Can you share more details regarding your workflow and what you are looking to accomplish? While we don’t have registration a dedicated field for paid registrants that is reported on, there are alternatives you can consider. For example, perhaps you can repurpose a webinar status to signify paid or not. Then place the webinar registration behind a paywall. By doing this anyone who registers can fall under the paid classification.