I just received this error as well, 3 days ago I posted at this forum post: https://forum.mendix.com/link/questions/87024.
Edit: I see that the GeoCoder.java from the Google Maps module is not using an API key for the request.
Edit 2: Download the latest Google Maps module from the app store, https://appstore.home.mendix.com/link/app/174/Mendix/Google-Maps-Module. Now it provides a constant for the API key.
Thanks for the reply, sorry what does no wit provide, as i can't seem to find it on that link.