Ionic push notification problem


I follow the tutorial to push notification, sometimes when I execute the follow command in terminal

curl -u xxxxxxxx: -H "Content-Type: application/json" -H "X-Ionic-Application-Id: xxxxxxx" -d '{"tokens":["xxxxxxxx"],"notification":{"alert":"I come from planet Ion."}}'

I got this error message:

<!DOCTYPE html>
      <meta name="viewport" content="width=device-width, initial-scale=1">
      <style type="text/css">
        html, body, iframe { margin: 0; padding: 0; height: 100%; }
        iframe { display: block; width: 100%; border: none; }
    <title>Application Error</title>
      <iframe src="//">
        <p>Application Error</p>

maybe something wrong in the api `

someone can give me a help? thanks.