WKUserContentController methods not called when after url change

Question

I have a WkWebView where I load my webpage. The webpage is a questionnaire so there are several steps with questions and on final page I get the result. I want to detect when user is at the final page. The web page uses postMessage to send data. To get this change I have implemented webview with WKUserContentController like following:

private lazy var webView: WKWebView = {
        let config = WKWebViewConfiguration()
        let source = """
            window.addEventListener('message', function(e) {
                window.webkit.messageHandlers.message.postMessage(JSON.stringify(e.data));
            });
            """
            let script = WKUserScript(source: source, injectionTime: .atDocumentEnd, forMainFrameOnly: false)
//            let script = WKUserScript(source: "alert('Hello, World!');", injectionTime: .atDocumentEnd, forMainFrameOnly: false)
            config.userContentController.addUserScript(script)
            config.userContentController.add(self, name: "message")
        
        webView = WKWebView(frame: .zero, configuration: config)
        
        webView.translatesAutoresizingMaskIntoConstraints = false
        webView.addObserver(self, forKeyPath: "URL", options: .new, context: nil)
        webView.navigationDelegate = self
        return webView
    }()
func userContentController(_ userContentController: WKUserContentController, didReceive message: WKScriptMessage) {
        print(message)
        print(message.name)
        guard let dict = message.body as? [String : AnyObject] else {
            return
        }
        print(dict)
    }

WKUserContentController, didReceive message is called on load of the web page but it is not called after subsequent url changes