flutter program work okay on chrome, but cannot work correctly on web server

I'm pretty new to flutter, and wrote the following flutter program to get the client IP address and location. I'm calling "http://ip-api.com/json" for IP address and location information. The program works okay by using device "chrome", I can print client's IP address on the title bar.
. When I switch to device "web server", and the program print nothing on the title bar, and it just show a blank page. I have been struggle on this for a week now. Is this because that flutter is still in beta version for web support? Your help is highly appreciated.

import 'dart:async';
import 'dart:convert';
import 'package:flutter/material.dart';
import 'package:http/http.dart' as http;

class IP_info{
  final String IP;
  final String city;
  final String ZIP;
  final String st_code;
  final String state_name;
  final String country_code;
  final String country_name;

IP_info({this.IP,this.city,this.st_code,this.ZIP,
this.state_name,this.country_code,this.country_name});



factory IP_info.fromJson(Map<String, dynamic> json){
    return IP_info(
      IP:json['query'],
      ZIP:json['zip'],
      city:json['city'],
      country_code:json['countryCode'],
      st_code:json['region'],
      country_name:json['country_name'],
      state_name:json['regionName'],
    );
  }
  }
}

void main() {
  runApp(MaterialApp(
      title: 'This is a test',
      home: MyApp()
  ),
  );
}

class MyApp extends StatefulWidget{
  @override
  State<StatefulWidget> createState()  => MyAppState();
}

class MyAppState extends State<MyApp> {

  bool _isLoading = false;
  IP_info ip_info;

  @override
  void initState() {
     _isLoading=true;
    _getPublicIP();
  }

_getPublicIP() async {
    try {

      const url = 'http://ip-api.com/json';

      final response = await http.get(url);
      if (response.statusCode == 200) {
        ip_info = IP_info.fromJson(json.decode(response.body));

        setState(() {
          _isLoading = false;
        });
        }
      else {
        // The request failed with a non-200 code
        print(response.statusCode);
        print(response.body);
      }
    } catch (e) {
      print(e);
    }

  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text('Testing your IP Address ${ip_info.IP}'),),
    );
  }
 }