Could not display interface. Please check definition and inputs. Interface Definition: Expression evaluation error at function a!forEach [line 3]: Error in a!forEach() expression during iteration 1: Expression evaluation error at function a!isNotNullOrEmpt

What kind of data does that expression return? Is that a list of records?

Yes, it is a list of records

In that expression, do you also fetch the related data you try to index later?

In that expression, do you also fetch the related data you try to index later?