Featured Image Doesn't Show On Map

Hi there,

I was wondering if I used an incorrect combination of shortcodes to display the featured image on my post geotag map.

I created a page where I want to display a map with all the posts shown as a marker using this addon: Geotag my posts. Which works fine. I also have Additional Behaviors on which also works. But somehow I can't get the posts featured image to show on the marker popup.

This is the shortcode I used on the page:
[agm_gwp_geocoded_posts is_responsive="true" query="post_type=posts" overlay="yes" featured_image="yes"]

And you can see it live here:

Any advice on how to get the marker popup to show the featured image of the post?