When the Wikitude SDK uses ARKit in the background for tracking, it first tries to initialize a plane on which to place the content. This error message indicates that no such plane could be found, so tracking cannot start. Please try to move the device sideways while looking at a planar surface and then tracking should start. The grid color will also change from orange to green when it is safe to start.
In case you still have difficulties with getting the sample to run, please let us know.
According to your documentation, smart tracking should be working on devices supporting ARKIT and it should be using ARKit instead of your tracking algorithm.
I have downloaded the Unity package for Professionals and open your sample project.
I build it on my device IPhone 11 Pro.
I have managed to build samples project successfully, but when I start Instant Tracking Scene I got this error in the Xcode console -
ERROR: [Runtime][00:03:35.902.567] > ARKit tracking can not be started. (code 1007) (underlying error: Could not find a plane. (code 1002))
>ERROR: [Runtime][00:03:35.919.240] > Could not find a plane. (code 1002)
Wikitude SDK Professional Package 9.8
Xcode version: 12:4
IPhone 11 Pro - iOS 14.4.2