I feel dumb for asking this, but how do you refer to items in a group layer in Arcade?

This was my code, and it worked great until I popped the PDFO_Permitee_List into a group layer.
FeatureSetByName($map, 'PDFO_Permitee_List', includedFields)
I've tried both "PDFO Range\PDFO_Permitee_List", "PDFO Range/PDFO_Permitee_List" and just to be safe, "PDFO Range\\PDFO_Permitee_List".
What am I missing here?