Since Google maps has changed the standard plan policy on June 22, 2016 requiring the API key to make the map work: https://googlegeodevelopers.blogspot.com.au/2016/06/building-for-scale-updates-to-google.html This feature has been integrated into each theme update. So the steps below will help you to get rid of the error and make the map work on your website:
For WP Themes
1. Make sure you use the most recent theme version. Check the ‘Change log’ section on the theme description page to find out about the last version release.
2. Generate the Google Map API key following this link https://support.imithemes.com/knowledgebase/get-google-maps-api/
3. Navigate to Theme Options -> Map API in your WP admin. With that done, if the API key is generated properly, you will see the map working on the site.
For HTML Templates
Look for the script loading in your pages HTML code and search for:
Change it to:
<script src="http://maps.googleapis.com/maps/api/js?sensor=false&key=ENTER YOUR GENERATED API KEY HERE"></script>
Here after key= enter your API key generated for maps. Generate the Google Map API key following this link https://support.imithemes.com/knowledgebase/get-google-maps-api/