Why is this javascript code is unable to send data to this flutter web page on local host?

I am developing a project on ecommerce where i have need of sending the data from html to flutter web page using javascript. I tried ways of sending data using EncodedURIComponent to creating a web socket to send data to the flutter site. But, none of that work . Can somebody tell me how to send data from a html site to flutter web page using javascript?

params.id is the value that want to send.

//sample js and dart code

//js

 function sendData() {
        const id = `${params.id}`; // Example ID
    

        // Construct the URL with query parameters
        const flutterUrl = `http://localhost:50759/#/productbrand?id=${encodeURIComponent(id)}}`;
        
        // Redirect to the Flutter web app with the query parameters
        window.location.href = flutterUrl;
    }
      document
        .getElementById("send-product-id")
        .addEventListener("click", sendData);

//dart
this one is the route code where i have already given required parameter in the ui file.

case productbrand:
    final id = uri.queryParameters['id'];
    return MaterialPageRoute(
      builder: (_) => Productbrandpage(id: id ?? 'Unknown ID'),
    );

I have a route name code which put up a name for each page displayed in the search bar.

 Productbrandpage.route: (context) => Productbrandpage(
    id: '',
  ),

Thank you.