Permissions
The Zappar for Unity package needs to ask the user for permission to access the camera and motion sensors on the device. A function is set up in the ZapparCamera.cs script that will automatically show a built-in UI informing the user of the need and providing a button to trigger the browser's permission prompts. Once the user permissions are granted the experience will run.
If you'd rather show your own permissions UI, you can turn off the standard Zappar permissions by un-checking the Permission UI (WebGL) parameter in the Zappar Universal AR Project Settings.
You can then develop your own custom, permissions UI and functionality.
Please note - due to browser restrictions, this function must be called from within a user event on the HTML canvas. A standard Unity button component will not work.