MBurger Engagement platform uses FCM (Firebase Cloud Messaging) so send push notifications. If you wish to add this feature to your app you should before follow these steps regarding FCM configuration:
Create a Firebase project by visiting this page and clicking on "Add Project"
Inside the project create your Android app by clicking "Add App" and follow the instructions, resulting in downloading a .json configuration file to move in your app folder.
Go to the project settings clicking on the gear on the left-top part of the page:
On the Settings page click on "Cloud Messaging" and copy the "Server Key" you see right below the tab
Paste the token on MBurger Engagement Platform Settings FCM box and click "Update"