User must be on whitelist error when using Facebook Ad Insights API – Facebook api

Why does my query to the Ad Insights API result in the following response?

https://graph.facebook.com/v2.9/<ad_id>/insights?access_token=<access_token>&fields=...

{
   "error": {
      "message": "(#3) User must be on whitelist",
      "type": "OAuthException",
      "code": 3,
      "fbtrace_id": "..........."
   }
}