Scene working in Simulation View but not with webcam / android


I've built a simple scene with a MARS Session object and an Image Marker using the MARS presets.
In the Image Marker I've set an image and connected the Session to a Marker Library using a tutorial.
I added the image to the Marker Library SO and gave it its dimension (0.03m X 0.015m).
I added a cube as a child to the marker for testing.

When I play in the Simulation View, and walk around in Device View, I see the cube popping up as expected. When I swtich over to Video Feed and use my webcam, I don't see the cube when I go over the image in real life (I printed it to fit the dimensions). It seems that Unity does not capture the image no matter how near / far it is, even with right the focus right on the image.

I've built the project to Android and am using a Galaxy S21 smartphone, with the same results.

I'm using Unity 2021.3.13f
MARS 1.5.0
ARFoundation 4.2.7
ARFoundation Providers 1.5.0
ARCore XR Plugin 4.2.7

(Burst 1.6.6)

Can anyone help me understand what can I do to have the image marker work?

cool but no one asked