if you run your request in a web browser, do you see anything back?
looking at Google API doc they say you need to send an HTTPS request equivalent to that CURL
curl -X POST "https://www.googleapis.com/geolocation/v1/geolocate?key=YOUR_API_KEY" \
-H "Content-Type: application/json" \
-d \
'{ "homeMobileCountryCode":310,
"homeMobileNetworkCode":410,
"radioType":"gsm",
"carrier":"Vodafone",
"considerIp":true
}'