Bug Adding images to Images tracker

Hi,

I'm trying to add images on runtime to be recognized by Image tracker. I'm following the tutorial:
https://docs.unity3d.com/Packages/com.unity.xr.arfoundation@4.0/manual/tracked-image-manager.html

But an error is thrown in this line:

trackImageManager.referenceLibrary = trackImageManager.CreateRuntimeLibrary(xrReferenceImageLibrary);

the error is exactly in this line of ARTrackedImageManager.cs:

if (subsystem == null)
throw new NotSupportedException("No image tracking subsystem found. This usually means image tracking is not supported.");

It seams to tell that image tracking is not supported. But if I try to track image added in the XRReferenceImageLibrary in the editor, it is working fine. Then I understand that the image tracking is supported and working well.

I'm developing an aplication for Android ARMv7 using as a target System: Android Oreo 8.1, and I'm using Unity in the version 2020.2.7f1 and the verison of AR Foundation 4.1.13

Thanks in advance!!!!!
Daniel