Essentially you now have to get a Key if you dont already have one and activate the Google Maps APIs on it, including Maps & Geocoding. Then you'll need to setup billing with google and give them a credit card.
When you enable billing, you get $200 free usage every month for Maps, Routes, or Places. Based on the millions of users using Google APIs today, most of them can continue to use Google Maps Platform for free with this credit.
You only pay for what you use. You can review rates and access your spending any time in your Google Cloud Platform Console, where you can also set daily quotas to protect against unexpected increases. You can also set billing alerts to receive email notifications, when charges reach a preset threshold determined by you.