As of July 16, 2018, Google will charge for the use of it's Google Maps API functionality.
For a complete summary of the changes visit https://cloud.google.com/maps-platform/user-guide/pricing-changes. A brief explanation of the changes is outlined below.
Each month clients who use Google Maps on their websites will receive a $200 credit from Google to cover the use of the Google Maps plugin. Once that initial $200 credit from Google is completely used for the month, Google will charge Phosphor for the ongoing use of the Google Maps API for that month, after which, the $200 credit will renew. If you go over the $200, Phosphor will be charged for the overage and we will charge that cost back to you at the end of the month.
Costs are incurred for each map load, and the cost differs for the kind of map that is loaded (static, dynamic, street view). The free, $200 credit from Google can cover 100,000 static map loads, and 28,000 dynamic page loads which according to Google should be enough to cover most websites.