Specify a Custom Notification Sound for iOS Push Notifications

This feature uses a sound included in your mobile app as a custom audio signal when a push message arrives on the mobile device.

Add a file named custom.caf to your project. The cloud push payload looks for a file named custom.caf.
Add the custom.caf audio file to the Copy Bundle Resources folder in Xcode for your app.
To prevent Xcode from using cached files, perform a clean build of the folder in Xcode. In the Product menu, hold the Option key and select Clean Build Folder.