Phone don't receive notification from FCM server

Question

I am trying to send notifications from a node server. I am using this code (which I got from reading this post):

request({
   url: 'https://fcm.googleapis.com/fcm/send',
   method: 'POST',
   headers: {
     'Content-Type' : 'application/json',
     'Authorization': 'key=MY_SERVER_KEY'
   },
   body: JSON.stringify(
     { data: {
         message: "Something delicious"
       },
       to: "DEVICE TOKEN"
     }
   )
 }, function(error, response, body) {
   if (error) {
     console.error(error)
   }
   else if (response.statusCode >= 400) {
     console.error('HTTP Error: ' + response.statusCode + ' - ' + response.statusMessage)
   }
   else {
     console.log('Message sent')
   }
 })

It responds with Message sent, but I never receive an notification on my developer phone.

It works just fine when I am sending directly from Notifications tab in Firebase console.

What could I be doing wrong here?