Why is the toolbar not showing when I tap on the textfield?

I would like to implement a done toolbar above the numpad keyboard when the textfield is tapped however the toolbar is not showing up for some reason.

The following code sample has been used:

extension UITextField{

    @IBInspectable var doneAccessory: Bool{
        get{
            return self.doneAccessory
        }
        set (hasDone) {
            if hasDone{
                addDoneButtonOnKeyboard()
            }
        }
    }

    func addDoneButtonOnKeyboard()
    {
        let doneToolbar: UIToolbar = UIToolbar(frame: CGRect.init(x: 0, y: 0, width: UIScreen.main.bounds.width, height: 50))
        doneToolbar.barStyle = .default

        let flexSpace = UIBarButtonItem(barButtonSystemItem: .flexibleSpace, target: nil, action: nil)
        let done: UIBarButtonItem = UIBarButtonItem(title: "Done", style: .done, target: self, action: #selector(self.doneButtonAction))

        let items = [flexSpace, done]
        doneToolbar.items = items
        doneToolbar.sizeToFit()

        self.inputAccessoryView = doneToolbar
    }

    @objc func doneButtonAction()
    {
        self.resignFirstResponder()
    }
}

Make sure in your storyboard, TextField's property inspector doneAccessory property is set to ON

and O/P looks like