What is the `Authorization` part of the http post request of Google's Firebase Downstream message?

Question

I want to try to send a message using google\'s FCM messaging service and as the document says, the http request should be something like this:

Answer 1

This is your Server key which you can observe into console.developers.google.com or Firebase project console under Project Settings > Cloud Messaging. Note the key it's auto created by Google Services. You ought add IP Address inco G.Console to restrict usage.

Plus do remember about Content-Type: application/json, otherwise you will get Error=MissingRegistration.