Line Renderer / XR Line Renderer not working on Google Cardboard?

Hello,

I'm using the latest Google Cardboard SDK for Unity (reference: https://github.com/googlevr/cardboard-xr-plugin ) with Unity 2019.3

This SDK doesn't have the handy reticle Daydream had, so I'm trying to recreate a simple one that I can use across my projects. I've tryed to draw a circle using Line Renderer: it shows on editor, but it doesn't on the phone.

There is also XR Line Renderer ( https://github.com/Unity-Technologies/XRLineRenderer ) again, I can create a beautiful circle, but it doesn't show up on the phone.

What am I missing? In alternative, how would you suggest to recreate the reticle Daydream had?

Thanks in advance.