Starting June 16, 2018, a new Pay-As-You-Go model for Google Map APIs will be implemented. This well give the users versatility and control when it comes to using the APIs. Users can use as much as needed and pay for the usage per month.
Before this change, Standard use for Google Map APIs is free until 25,000 requests per day. Going over the standard use, the price would depend on the volume set for use.
For the new Pay-As-You-Go model, the Google Maps Platform APIs are billed by SKU (Stock Keeping Unit).
Tracking is done on each product SKU’s usage. It’s calculated by: SKU Usage x Price per use. 
As of July 16, 2018, to continue to use the Google Maps Platform APIs, you must enable billing on each of your projects. If you choose not to add a billing account, your maps will be degraded, or other Maps API requests will return an error.
For more information on the new Pay-As-You-Go model for Google Map APIs: