How do I create an association filter in a Gallery?

Hey, I need to add a drop down filter for my gallery view, with which I can filter the results based on an associated “topic” entity. As you can see (highlighted in green) the necessary attribute is selected in the filtering options:   However, the drop down filter displays the following error message:   This seems odd to me, because I read on the Mendix website, in the module description that association filtering is possible: Any idea, how I can fix this problem? (And would there also be a way to filter *-* associations?)
1 answers

Have you selected the association to filter on, or an attribute of the associated object? I can't see the end of the attribute you filled out so it's hard to tell from the screenshot.