objectWillChange.sink why not working in swift

I am a Swift beginner; This code in my AppDelegate, it's working!

func applicationDidFinishLaunching(_ notification: Notification) {
    var join = Contact.instance
    var cancellable = Contact.instance.objectWillChange.sink { val in
      print("val: \(val)")
      print("\(join.age) will change")
    }
    print(join.haveBirthday())
  }
// val: ()
// 24 will change
// 25

But, Call havBirthday() from inside ContentView, it's not working. There is no output from the console.

struct ContentView: View {
   
  var timer = Timer.publish(every: 1, tolerance: nil, on: .current, in: .common, options: nil).autoconnect();
   
  var body: some View {
    VStack{
      Text("The name is: \(Contact.instance.name), and age is \(Contact.instance.age)")
        .padding()
      Button("age+1"){
        let age = Contact.instance.haveBirthday()
        print("changedAge: \(age)")
      }
    }
  }
}

class Contact: ObservableObject{
  static let instance = Contact(name:"John Appleseed",age:24)
   
  @Published var name: String;
  @Published var age: Int;
   
  init(name:String, age:Int){
    self.name = name;
    self.age = age;
  }
   
  func haveBirthday()->Int{
    age+=1;
    return age;
  }
}