This may be slightly different, but I have been trying to do the same kind of thing using “Advanced Content Type”. Evidently PODS doesn’t support relationships between “external” tables, only between core WP entities. No matter what I do I get “No Related Fields Found”.
I ran across something related to this subject at the link below. It’s a couple of years old. The author mentions “the example code below“, but there’s nothing there. Maybe he forgot to post it.
https://pods.io/tutorials/get-values-from-a-custom-relationship-field/
It looks as if this has been a known limitation for some time (years?)
Good luck.
