WP All Import's add-ons have a specific field that you must put your Google API Key in: https://d.pr/i/eeum5M. If you don't already have one, here's how to get a key: https://developers.google.com/maps/documentation/geocoding/get-api-key.
Log in at https://console.cloud.google.com, go to "APIs & Services", click "Credentials", click your API key and make sure "Application restrictions" is either set to "None" or "IP addresses (web servers, cron jobs, etc.)" with your web servers IP address added.
Log in at https://console.cloud.google.com, go to "APIs & Services" on the left, click "ENABLE APIS AND SERVICES", then search for "Geocoding API" and make sure it's enabled for your key.
To test your key and make sure it's working, copy the following URL into your favorite text editor:
https://maps.googleapis.com/maps/api/geocode/json?address=1600+Amphitheatre+Parkway,+Mountain+View,+CA&key=YOUR_API_KEY
Replace YOUR_API_KEY with your Google API key, then visit the URL in your web browser. If you see address data then you'll know it's working.