1st Message Title Section in your firebase cloud messaging page is called Notification Data[when the App is minimized or closed it will be shown as a notification]

2nd Message Title section which is in the bottom of the webpage is called Message Data, [it will be shown In inside app as a notification or an Alert dialogue that's up to your wish]

STEPS Create a dummy Project then use firebase message plugin, and in that Box give BMW Cars as atopic and click subscribe

Now go to your console then send a message with the FOLLOWING FORMAT it must contain Id and Status keys because we are parsing the Id and Status Keys in order to show NextPage with the Status Key's Value but if u prefer a field like title or body then u can do that too but make sure to parse the map value in ur flutter code.