To use google maps two api keys are required. One for the client side map, and one for the back end geocoding. The back end key only needs access to In mysite/_config/settings.yml
Dynamic\SilverStripeGeocoder\GoogleGeocoder:
geocoder_api_key: BACK_END_API_KEY
map_api_key: FRONT_END_API_KEY
Replace BACK_END_API_KEY
with your google maps api key that is restricted by ip.
Replace FRONT_END_API_KEY
with your google maps api key that is restricted by referrer.
If you are unsure where to get an api key, look here.