NSViewRepresentable control not being updated until resize of form

I have created a wrapped NSTextField to allow for keystroke validation.

Code Block Swift
class ValidatableTextField: NSTextField, NSTextViewDelegate
{
  var validationClosure: ((ValidatableTextField, NSRange, String?) -> Bool)?
  func textView(_ textView: NSTextView, shouldChangeTextIn affectedCharRange: NSRange, replacementString: String?) -> Bool
  {
    return validationClosure?(self, affectedCharRange, replacementString) ?? true
  }
}
struct CurrencyTextField<rootT : AnyObject, valueT> : NSViewRepresentable
{
  private var object: rootT?
  private var keyPath: ReferenceWritableKeyPath<rootT, valueT>?
 
  func makeCoordinator() -> Coordinator
  {
    return Coordinator(object, keyPath: keyPath)
  }
  init(object: rootT?, keyPath: ReferenceWritableKeyPath<rootT, valueT>?)
  {
    self.object = object
    self.keyPath = keyPath
  }
  func makeNSView(context: Context) -> ValidatableTextField
  {
    let textField = ValidatableTextField()
    textField.validationClosure = context.coordinator.validationClosure
  
    return textField
  }
  func updateNSView(_ nsView: ValidatableTextField, context: Context)
  {
    guard let object = object,
          let keyPath = keyPath else
    {
      return
    }
    nsView.stringValue = "\(object[keyPath: keyPath])"
  }
  class Coordinator : NSObject
  {
    var object: rootT?
    var keyPath: ReferenceWritableKeyPath<rootT, valueT>?
    init(_ object: rootT?, keyPath: ReferenceWritableKeyPath<rootT, valueT>?)
    {
      self.object = object
      self.keyPath = keyPath
    }
    lazy var validationClosure: ((ValidatableTextField, NSRange, String?) -> Bool) =
    {
      textField, range, replacementString in
      if replacementString!.isEmpty
      {
        return true
      }
      return replacementString?.contains(where:
      {
        (char: Character) -> Bool in
        return char.isNumber || String(char) == Locale.autoupdatingCurrent.decimalSeparator
      }) ?? false
    }
  }
}
struct ContentView: View
{
  @ObservedObject var person: Person
  var body: some View
  {
    VStack
    {
      Spacer()
      Text(person.name)
      HStack
      {
        Spacer(minLength: 100)
        CurrencyTextField<Person, Double>(object: person, keyPath: \.bankBalance)
        Text("\(person.bankBalance)")
        Spacer(minLength: 100)
      }
      Button(action:
      {
        self.person.bankBalance = 65.43
      })
      {
        Text("Change bank balance")
      }
      Spacer()
    }
  }
}

My problem is that I am setting the bankBalance property on the Person and the Text next to the TextField is being updated but my CurrencyTextField is not.

I may have 30 years of programming experience, including quite a few with Swift but SwiftUI, beyond the simplest of examples, is proving a bit difficult. What am I missing here please?