In mid 2016, Google changed its API settings and now requires a user to sign up for a Maps API key before using it's Google Maps service.
Scroll down to the heading "Get A Key" and following the instructions there.
When you have finished doing this, the the following;
1) Go back to the site builder and click on the Modules tab.
2) Scroll all the way to the right-most option and click on the Script button.
3) Drag this module to all the pages where your have a map module and insert the following code
<script async defer src="https://maps.googleapis.com/maps/api/js?key=YOUR_API_KEY&callback=initMap"