Default sound playing on push notification but not custom sound

I’m doing a few tests with push notifications with firebase.

Everything is working fine except the custom sound that I’m trying to set. It’s always the default sound which is playing.

    platform.ready().then(() => {
        .then(token => console.log(`The token is ${token}`))
        .catch(error => console.error('Error getting token', error));

        this.firebase.onNotificationOpen().subscribe((response) => {
          console.log("RECEIVED APP NOT OPEN")
          console.log("RECEIVED APP OPEN");

And here is the POST that I’m sending.

  "to" : "f1oXvN6v9W...",

  "notification" : {
    "body" : "an amazing body",
    "title" : "an amazing title",
    "sound" : "alarm" // I also tried with alarm.mp3

Of course, I put the file alarm.mp3 in platforms/android/app/src/main/res/raw/alarm.mp3

What am I missing ?

You managed to solve it, I have the same problem.