I tried to get total_video_views_by_country_id from the Facebook Graph API and have some error

I tried to get total_video_views_by_country_id from the Facebook Graph API using the endpoint

GET /v20.0/{video-id}/video_insights HTTP/1.1 

via the Graph API Explorer 510171338137924/video_insights/metric=total_video_views_by_country_id
However, when I attempted this on the Graph API Explorer, the result was

{
  "error": {
    "message": "(#100) The value must be a valid insights metric",
    "type": "OAuthException",
    "code": 100,
    "fbtrace_id": "AA1wczXhtw-h7XE8msmeQgY"
  }
}