Add-method isn't working in Main

Here’s a gist of my project:

This class represents a book with chapters, pages, an index, a table of contents etc.
I wrote an adder in the Index class to add an index entry (“eintrag”)

public void addIndexEintrag (IndexEintrag eintrag) {

auflistung is a list of index entries that constitutes the index.

but if I call teh adder in main, it isn’t recognized:

auflistung1.addIndexeintrag(eintrag1); //IntelliJ says "cannot resolve method"
Compiler output for this is cannot find smybol

on the other hand, this works: