Calling Youtube API for user Channels returns authorizationRequired

I am trying to call Youtube API for user Channels:

https://content-youtube.googleapis.com/youtube/v3/channels?part=snippet&part=statistics&mine=true&key=AIXXXXX

It returns the following response:

{"error": {"code": 401,"message": "The request uses the \u003ccode\u003emine\u003c/code\u003e parameter but is not properly authorized.","errors": [      {"message": "The request uses the \u003ccode\u003emine\u003c/code\u003e parameter but is not properly authorized.","domain": "youtube.parameter","reason": "authorizationRequired","location": "mine","locationType": "parameter"      }    ]  }}

I haven't been able to find a proper answer on stackoverflow or on youtube documentation to overcome this issue. Any help is greatly appreciated.