After you follow the Google guide on how to generate such a key, navigate to Listing Types Settings Integration Maps and insert your key into the field Google map API key, then save the changes.
Back to your Google Developers Console, make sure that you have the following APIs enabled:
- Places API
- Geocoding API
- Apart from the APIs, make sure that you have a valid billing method, otherwise your request won’t be approved.
Google Maps are not a free service. They will give you some free views each month, but when you start getting some serious traffic, it will start charging you, using your primary billing method.
Here you can check the pricing options.