Metaball(t)... super simple question

I am trying to use Metaball(t) on my own 2 faces/surfacs, but I cannot get any curve to show…
I am looking at a simple tutorial, but I need some help, unfortunately.

What plane do I feed to the metaball(t) node to “find” the two faces to use?

please right click on this:

choose “internalise data”, save the file and post that gh file

Thank you inno, I used the PlaneFit node to find the plane for each of my faces (after deconstructing Breps).

Then, tweaking the tolerance values to a tiny value I begun to get some results.