In order to have access to Zoom's API, you need to be on one of their paid plans.
Zoom does not notify Zapier of new registrants if those were created via their API, e.g. with another Zap. As a workaround, they suggest "to send the Zoom registration information to a web/smart form to capture the data. Then, you can leverage this form data to push out the registration information when a new form/submission is added.".
Alternatively, this may be due to Zoom not supporting recurring webinar registration with Zapier yet. This is currently being worked on but there is not an ETA on when this will be available.
Duration field for the "Create Meeting" Action is in minutes, not hours.
Please refer to this Zoom guide for more details: https://support.zoom.us/hc/en-us/articles/205260649-How-To-Use-Zapier