flutter webview App not working call function on flutter app

Question

not working call function on flutter app showing net:err_unknown_url_scheme on click call button site or not opening call dialer app showing net:err_unknown_url_scheme

main.dart page

import 'package:flutter/material.dart';
import 'package:web_view/pages/UrlLaunch.dart';
void main() {
runApp(const MyApp());
 }

class MyApp extends StatefulWidget {
const MyApp({Key? key}) : super(key: key);

 @override
 State<MyApp> createState() => _MyAppState();
  }

 class _MyAppState extends State<MyApp> {
@override
 Widget build(BuildContext context) {
 // ignore: prefer_const_constructors
 return MaterialApp(
  debugShowCheckedModeBanner: false,
  title: 'Real Manager',
  // ignore: prefer_const_constructors
  home: UrlPage(),
  // ignore: prefer_const_constructors
  
     );
   }
  }

UrlLaunch.dart page

import 'package:flutter/material.dart';
// ignore: unused_import
import 'package:http/http.dart';
 // ignore: unused_import
import 'package:url_launcher/url_launcher.dart';
import 'package:webview_flutter/webview_flutter.dart';

class UrlPage extends StatefulWidget {
const UrlPage({Key? key}) : super(key: key);

@override
State<UrlPage> createState() => _UrlPageState();
 }

class _UrlPageState extends State<UrlPage> {
 @override
 Widget build(BuildContext context) {
String url = 'https://development.realmanager.in/Management/index.php';
return Scaffold(
    appBar: AppBar(
      title: const Text('Welcome to Real Manager'),
    ),
    body: WebView(
        javascriptMode: JavascriptMode.unrestricted,
        initialUrl: url,
        navigationDelegate: (request) async {
          if (request.url.startsWith('tel:')) {
            launch('tel:01761685693');
            return NavigationDecision.prevent;
          } else {
            throw 'Could not launch $url';
          }
         })

    
        );
       }
      }

not working call function on flutter app showing net:err_unknown_url_scheme on click call button site or not opening call dialer app showing net:err_unknown_url_scheme