GMail API getting Access Not Configured in Android

Question

Hi i am trying to implement GMail API in my android app to send mail in background. But i am getting a response like this. Even if I enabled Gmail API permission in my app.

{
      "code" : 403,
      "errors" : [ {
        "domain" : "usageLimits",
        "message" : "Access Not Configured. The API (Gmail API) is not enabled for your project. Please use the Google Developers Console to update your configuration.",
        "reason" : "accessNotConfigured",
        "extendedHelp" : "https://console.developers.google.com"
      } ],
      "message" : "Access Not Configured. The API (Gmail API) is not enabled for your project. Please use the Google Developers Console to update your configuration."
    }

I followed https://developers.google.com/gmail/api/quickstart/android for integrating.