No notification sound when sending notification from firebase in android

In the notification payload of the notification there is a sound key.

From the official documentation its use is:

Indicates a sound to play when the device receives a notification. Supports default or the filename of a sound resource bundled in the app. Sound files must reside in /res/raw/.

Eg:

{
    "to" : "bk3RNwTe3H0:CI2k_HHwgIpoDKCIZvvDMExUdFQ3P1...",

    "notification" : {
      "body" : "great match!",
      "title" : "Portugal vs. Denmark",
      "icon" : "myicon",
      "sound" : "mySound"
    }
  }

If you want to use default sound of the device, you should use: "sound": "default".

See this link for all possible keys in the payloads: https://firebase.google.com/docs/cloud-messaging/http-server-ref#notification-payload-support

For those who don't know firebase handles notifications differently when the app is in background. In this case the onMessageReceived function is not called.

When your app is in the background, Android directs notification messages to the system tray. A user tap on the notification opens the app launcher by default. This includes messages that contain both notification and data payload. In these cases, the notification is delivered to the device's system tray, and the data payload is delivered in the extras of the intent of your launcher Activity.

select advanced options when Write a message, and choose sound activated

this is My solution

Try this

{
    "to" : "DEVICE-TOKEN",

    "notification" : {
      "body"  : "NOTIFICATION BODY",
      "title" : "NOTIFICATION TITILE",
      "sound" : "default"
    }
  }

@note for custom notification sound:-> "sound" : "MyCustomeSound.wav"

The onMessageReceived method is fired only when app is in foreground or the notification payload only contains the data type.

From the Firebase docs

For downstream messaging, FCM provides two types of payload: notification and data.

For notification type, FCM automatically displays the message to end-user devices on behalf of the client app. Notifications have a predefined set of user-visible keys.
For data type, client app is responsible for processing data messages. Data messages have only custom key-value pairs.

Use notifications when you want FCM to handle displaying a notification on your client app's behalf. Use data messages when you want your app to handle the display or process the messages on your Android client app, or if you want to send messages to iOS devices when there is a direct FCM connection.

Further down the docs

App behaviour when receiving messages that include both notification and data payloads depends on whether the app is in the background or the foreground—essentially, whether or not it is active at the time of receipt.
When in the background, apps receive the notification payload in the notification tray, and only handle the data payload when the user taps on the notification.
When in the foreground, your app receives a message object with both payloads available.

If you are using the firebase console to send notifications, the payload will always contain the notification type. You have to use the Firebase API to send the notification with only the data type in the notification payload. That way your app is always notified when a new notification is received and the app can handle the notification payload.

If you want to play notification sound when app is in background using the conventional method, you need to add the sound parameter to the notification payload.