Google Places API - REQUEST_DENIED

This is actually (b): wrong key. Actually, you're using the wrong kind of key (from Sign Up for the Google Maps API which is only good for the JavaScript V2 API).

Please see Obtaining an API Key for how to get a new API key, of the new kind.

Edit: At the time this question arose, valid API keys that worked on Geocoding API did not work on Places API, but now seem to work fine. Looks like some issue on Google side.

I just got a REQUEST_DENIED response when making an autocomplete request in a Ruby app. It turned out that I had not specifically switched on the Places API in my google api console.

Go to: https://console.developers.google.com and login. In the left menu go to "APIs & auth" -> "APIs" Then find the "Places API" option and click on the status to the right to toggle it to "on"

This fixed the problem immediately for me.