Flutter when clicked button will POST data to API but fail - flutter

Question

I create food order app with flutter, but i found some error on my code when i try to create some button which works for POST data to API. I hope you guys can help me, your help is very useful for me, thank you
this is a response from API,
This is an example of the data that can be sent
{
"nominal_diskon": "50000",
"nominal_pesanan": "100000",
"items": [
{ "id": 1, "harga": 10000, "catatan": "Tes" },
{ "id": 2, "harga": 10000, "catatan": "Tes" },
{ "id": 3, "harga": 10000, "catatan": "Tes" }
]}
this is a transaction_service.dart
class TransactionService {
String baseUrl = 'https://tes-mobile.landa.id/api';
Future<bool> checkout(
double diskon, double totalprice, List<MenuModel> menus) async {
var url = '$baseUrl/order';
var body = jsonEncode(
{
'nominal_diskon': diskon,
'nominal_pesanan': totalprice,
'items': menus
.map(
(menu) =>
{'id': menu.id, 'harga': menu.harga, 'catatan': menu.catatan},
)
.toList(),
},
);
var response = await http.post(
Uri.parse(url),
body: body,
);
print(response.body);
if (response.statusCode == 200) {
return true;
} else {
throw Exception('Gagal Melakukan Checkout!');
}
}
}
this is a transaction_provider.dart
class TransactionProvider with ChangeNotifier {
Future<bool> checkout(
double diskon, double totalprice, List<MenuModel> menus) async {
try {
if (await TransactionService().checkout(diskon, totalprice, menus)) {
return true;
} else {
return false;
}
} catch (e) {
print(e);
return false;
}
}
}
this is a home_page.dart which runs the button
class HomePage extends StatefulWidget {
#override
State<HomePage> createState() => _HomePageState();
}
class _HomePageState extends State<HomePage> {
String voucherCode = "";
#override
Widget build(BuildContext context) {
MenuProvider menuProvider = Provider.of<MenuProvider>(context);
VoucherProvider voucherProvider = Provider.of<VoucherProvider>(context);
TransactionProvider transactionProvider =
Provider.of<TransactionProvider>(context);
double hargaAkhir =
menuProvider.totalPrice() - voucherProvider.diskonHarga();
handleCheckout() async {
if (await transactionProvider.checkout(
10000,
100000,
menuProvider.menus,
)) {
Navigator.pushNamedAndRemoveUntil(
context, '/order-page', (route) => false);
}
}
Widget content() {
return ListView(
padding: EdgeInsets.symmetric(
horizontal: 25,
),
children: menuProvider.menus
.map(
(menu) => MenuCard(menu),
)
.toList(),
);
}
Widget customBottomNav() {
...
child: RaisedButton(
onPressed: handleCheckout,
child: Text('Pesan Sekarang',
style: whiteTextStyle.copyWith(
fontWeight: bold, fontSize: 14)),
color: menuProvider.totalItems() >= 1
? kPrimaryColor
: kDarkGreyColor,
textColor: kWhiteColor,
shape: RoundedRectangleBorder(
borderRadius: BorderRadius.circular(25),
side: BorderSide(
color: menuProvider.totalItems() >= 1
? Color(0xFF00717F)
: kDarkGreyColor,
width: 1,
),
),
),
)
],
),
),
],
),
);
}
return MaterialApp(
home: Scaffold(
backgroundColor: kWhiteColor,
body: content(),
bottomNavigationBar: customBottomNav(),
));
}
}