Firebase not displaying rich push notification

I am using firebase notification in my application. I want to send rich notification but firebase console don't have UI for same. So I am trying to send the payload using postman.

I have created Notification Service Extension for handling content but it never gets called.

Deployment target in xCode is iOS 10.0 and iPad has iOS 11

Json payload(Not Working):

{
    "to":"/topics/dev_news",
       "mutable_content": true,
       "data":
       {
         "attachment-url":"my image url",
         "media_type":"image"
   
       }
 }

FYI:

I am able to receive push if I add "notification" key-value in payload.

Json payload(Working but without media):

{
    "to":"/topics/dev_news",
       "mutable_content": true,
       "data": {
              "attachment-url":"my image url",
              "media_type":"image"
        },
       "notification" : {
             "title" : "demo push",
             "body" : "this is push body"
       }
 }   

Any idea about this??