iOS app - sync between macOS, iOS and watchOS

I have an app where I want to be able to sync data between macOS, iOS and watchOS in real-time.

I've already set up CloudKit and CoreData, however syncing between the elements is extremely slow and unreliable.

For this project, I will provide a Swift protocol that I would like you to use to create a CRUD interface with CloudKit authentication via Firebase, including security rules.

The database will look like:

struct List {

var title:String = ""
var icon:String = ""
var items:[Item] = [Item]()
var todoItems:[Item] = [Item]()
var completedItems:[Item] = [Item]()
}

struct Item {

var title:String = ""
var desc:String = ""
var completed:Bool = false
}

Please include *139* in your response if you have read this.