Ok, after many attempts, I realized that the "silent notification" only works if the device is wn Wifi or in Foreground. That is why I cannot play in "background" when on 4G.
If the notification is not silent, that is, I do it normal.
So if I receive the notification in the background regardless of whether I am on Wifi or 4G, the problem then is that the "Custom Sound" does not respect me.
The notification is received with the normal sound, and the mediaplayer runs until the application is opened.
Is there a way to change the remote notification sound?
Put a custom sound? I have done the tests in sending the "sound" parameter, but I can't make it change the default sound.
This post only works for local notifications.