Edit: The link below seems to be dead. You can read Google Maps Platform Billing‘s documentation here https://developers.google.com/maps/billing-and-pricing/billing#billing-in-the-console
Check if your project has a billing account associated to it. You can use this Google tool: https://mapsplatformtransition.withgoogle.com/
“This project does not have a billing account. You will need to add
billing information for this project to continue to use Google Maps
Platform. The first $200 of monthly usage is free. 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.”
It will list all your projects using Google Maps and tell you to “Add Billing” if the project status is not “in good shape”.