The goal of this guide is to enable Firebase Cloud Messaging and download the json file needed in order to configure Android push notifications.

From your project's Firebase console go to Cloud Messaging and tap on the Manage Service Accounts link.

You should be redirected to a different page (login may be required again), once you land on the Google Cloud page, click on CREATE SERVICE ACCOUNT under the Service Accounts tab.
 

Add a name and description (optional)

Add the Role "Firebase Cloud Messaging API Admin”

Complete the creation by tapping DONE

You should see a new line added on the list of services. TAP ON IT or select it and tap on Manage Access

Then ADD KEY → Create new key.
Select JSON and create to complete.

This process will generate a new key entry and download a json file to your local machine, this json file is required to properly setup Android push notifications.