title: instagram sandbox user invite sent but where does the user accept it?
body: <p>I am consuming the instagram and have been able to sent the invite to my second user.
  However when the second user logs in to this link:</p>
  
  <pre><code>https://www.instagram.com/oauth/authorize/?client_id=XXXXXXX&amp;redirect_uri=yyyyyyyyyyy://&amp;response_type=token
  </code></pre>
  
  <p>they just get </p>
  
  <p><code>{"code": 403, "error_type": "OAuthForbiddenException", "error_message": "You are not a sandbox user of this client"}</code></p>
  
  <p>I have also logged in as that user to the official instagram app and still I have no place to accept the invite. How do the sandbox users accept their invites to use my app?</p>