How to add custom sound in awesome notifications in iOS

Question

I'm using awesome_notifications package in pub dev and i successfully implemented this package in iOS and it is working perfectly well. Now the thing is i want custom sound play when notification receive in iOS physical device. I also added .aiff sound file inside Runner folder but no sound is coming when notification receives. Below is the sample dart code and what is missing link to implement custom sound notification in iOS.

await AwesomeNotifications().createNotification(
                        content: NotificationContent(
                            id: 1,
                            channelKey: 'basic_channel',
                            title: 'Test',
                            body: 'test',
                            customSound: 'notification.aiff',
                            notificationLayout: NotificationLayout.Default),
                        actionButtons: [
                          NotificationActionButton(
                              key: 'MARK_DONE', label: 'Mark Done'),
                        ]);