In order to play a sound when a user receives a particular Push notification on Android devices, it is necessary to include the sound file in the app’s raw folder. Then, you may pass a key/value pair with a Push notification that triggers the sound when a device receives it.
The key is ll_sound_filename and the value is the name of your Android resource in the raw folder. Eg:
One important caveat to note is that this process only works on OS versions less than Android O. In order to send a Push notification with a sound to Android O devices, you would include a sound as part of a Notification Channel, such that you may trigger a notification sound simply by specifying the proper channel.