are you working with nanoflows..?
if not, to work with the map related activity you should use nanoflow. Open the app store and download the the nanoflow named as “Nanoflow common”.
then try to use them on the call nanoflow event.
if you dont know how to do that, let me know.
these seems to work:
https://marketplace.mendix.com/link/component/114050
My Google Maps Custom Marker widget can do this for sure. It also allows for dragging the marker after dropping it.