About this "New Client Application Form Required" button in online booking set up:
This is more like an intake form for new client. If you turned on this button, new client (the client who is not in your system) will only be able to input their information and pet information, but NOT able to select time spot.
Once the client submitted information, a notification will be sent to you, once you approve, the client and pet profile will be added to your system automatically. And then you can create new appointment for the client.