Error sending notifications by FCM (Error 401 Authentication Key)

I am creating a progressive web application for mobile that accepts notifications and I am using Firebase (FCM). To be able to test it, I use postman as a server to send notifications to my application.

Shipping to: link

Headers:

Authorization: key=SERVER-KEY
Content-Type: application/json

Body:

{
    "notification": {
        "title": "Hello World",
        "body": "This is Message from Admin"
    },
    "to": "TOKEN-GENERADO"
}

And I receive the following error:

  

The request was missing an Authentication Key (FCM Token). Por favor,   refer to section "Authentication" of the FCM documentation, at    link . Error 401