Add custom ringtone option to ColorOS RingtoneManagers ringtone picker

Question

ColorOS (Oppo) offers the ability to select a custom ringtone from a file with its ringtone picker, but it does not work with my app.

You can see that feature here.

This is the code I'm using:

    Intent intent = new Intent(RingtoneManager.ACTION_RINGTONE_PICKER);
    intent.putExtra(RingtoneManager.EXTRA_RINGTONE_TYPE, RingtoneManager.TYPE_NOTIFICATION);
    intent.putExtra(RingtoneManager.EXTRA_RINGTONE_TITLE, "Select Ringtone");

    activity.startActivityForResult(intent, 1);

I think, I have to set a specific flag, which displays that option.

I've tried all the input options shown on Android Developers, but non of them worked.