The downstream messages are sent to users from the server on behalf of a client app. FCM messages can be divided into two categories: Notification Messages and Data Messages.  The notification messages are directly displayed to user. Some examples of the notification messages are alert messages, chat messages, or messages to notify client app to start some processing; let's message backups. The data messages need to be handled in your client app code. Some examples are chat messages or any messages specific to your app. We will talk more about these message types in the next section of FCM Messages.