Below are the instructions from Google:
Follow these steps to get an API key:
- Go to the Google API Console.
- From the dropdown, choose Create a Project and click Continue
- This process may take a minute. You will see some notifications and a spinning bell icon.
- Click What Credentials Do I Need?
- Under Get your Credentials, copy the API Key
Back in WordPress, paste the key into the Google Maps API Key field and Save your changes.