Code :


Widget: 
PaymentWidgetExamplePage(
user: user!,
inventryId: widget.inventryId,
quantity: widget.quantity,
product: widget.product,
orderId: orderId!,
)

Class:

class PaymentWidgetExamplePage extends StatefulWidget {
final User user;
final ProductProduct product;
final int quantity;
final String inventryId;
String orderId;
PaymentWidgetExamplePage({
Key? key,
required this.user,
required this.product,
required this.quantity,
required this.inventryId,
required this.orderId,
}) : super(key: key);
@override
State<PaymentWidgetExamplePage> createState() =>
_PaymentWidgetExamplePageState();
}
class _PaymentWidgetExamplePageState extends State<PaymentWidgetExamplePage> {
late PaymentWidget _paymentWidget;
PaymentMethodWidgetControl? _paymentMethodWidgetControl;
AgreementWidgetControl? _agreementWidgetControl;
bool loading = false;
@override
void initState() {
super.initState();
double total = widget.product.price * widget.quantity.toDouble();
double discountPercent = widget.product.productTax.toDouble();
num finalAmount = total * (1 - discountPercent / 100);
_paymentWidget = PaymentWidget(
clientKey: "TOSS_PAYMENT_KEY",
customerKey: widget.user.id,
);
_paymentWidget
.renderPaymentMethods(
selector: 'methods', amount: Amount(
value: finalAmount.round(),currency: Currency.KRW,
country: "KR",
),
options: RenderPaymentMethodsOptions(
variantKey: "gec",
),
)
.then((control) {
_paymentMethodWidgetControl = control;
}).catchError((e) {
debugPrint("Payment methods render error: $e");
});
_paymentWidget.renderAgreement(selector: 'agreement').then((control) {
_agreementWidgetControl = control;
}).catchError((e) {
debugPrint("Agreement render error: $e");
});
}
@override
Widget build(BuildContext context) {
return Column(
children: [
Container(
height: 300,
child: PaymentMethodWidget(
paymentWidget: _paymentWidget,
selector: 'methods',
),
),
Container(
height: 100,
child: AgreementWidget(
paymentWidget: _paymentWidget,
selector: 'agreement',
),
),
MyElevatedButton(
onPressed: loading ? null : _handlePayment,
child: Text(loading ? "pleasewait_loading".tr() : "order".tr()),
),
],
);
}
Future<void> _handlePayment() async {
if (widget.user.shipping.address.line1.isEmpty) {
showSnackBar(
context: context,
content: "enter_shipping_warning".tr(),
);
return;
}
setState(() {
loading = true;
});
try {
Result paymentResult = await _paymentWidget.requestPayment(
paymentInfo: PaymentInfo(
customerName: widget.user.name,
orderId: widget.orderId,
orderName: widget.product.name,
customerMobilePhone:  widget.user.contact.phone, 
showCustomerMobilePhone: true,
),
);
if (paymentResult.success != null) {
var confirm = await UserRepository().confirmPayment(
paymentResult.success!.amount,
paymentResult.success!.paymentKey,
paymentResult.success!.orderId,
);
if (confirm['status'] == true) {
statuscheck(confirm['data']['orderId']);
} else {
showSnackBar(context: context, content: confirm['data'].toString());
setState(() => loading = false);
Navigator.pop(context);
}
} else if (paymentResult.fail != null) {
showSnackBar(
context: context,
content: paymentResult.fail!.errorMessage.toString(),
);
setState(() => loading = false);
}
} catch (e) {
setState(() => loading = false);
showSnackBar(context: context, content: e.toString());
}
}
void statuscheck(String paymentId) async {
try {
var res = await UserRepository().getUser();
double total = widget.product.price * widget.quantity.toDouble();
double discountPercent = widget.product.productTax.toDouble();
num finalAmount = total * (1 - discountPercent / 100);
UserModel user = UserModel.fromJson(res['data']);
var submitRes = await UserRepository().submitOrder(
tabledata: [
{
"created_by": "653b481026c8b2e7afcc2dd2",
"business": widget.product.business,
"product": widget.product.id,
"item_no": 1,
"inventory": widget.inventryId,
"inventory_id": widget.inventryId,
"unit": widget.product.unitOfMeasurement,
"price": widget.product.price,
"quantity": widget.quantity,
"tax": widget.product.productTax,
"total": finalAmount,
"sku": widget.product.sku,
"item_name": widget.product.name,
}
],
paymentId: paymentId,
customerId: user.user.id,
podate: DateTime.now(),
deliverydate: DateTime.now(),
total: (widget.product.price * widget.quantity),
tax: widget.product.productTax,
assets: [
{"url": widget.product.assets.first.url, "type": "image"}
],
name: widget.product.name,
);
if (submitRes['status'] == true) {
Navigator.pushReplacement(
context,
MaterialPageRoute(
builder: (context) => OrderSuccess(
quantity: widget.quantity,
product: widget.product,
order: submitRes['data'],
),
),
);
} else {
showSnackBar(context: context, content: submitRes['message']);
setState(() {
loading = false;
Navigator.pop(context);
});
}
} catch (e) {
setState(() {
loading = false;
Navigator.pop(context);
});
}
}
}

Confirm Payment Code:

Future<Map<String, dynamic>> confirmPayment(
num amount, String paymentKey, String orderId) async {
try {
const String secretKey = 'TOSS_PAYMENT_KEY';
const String apiUrl = 'https://api.tosspayments.com/v1/payments/confirm';
final headers = {
'Authorization': 'Basic ${base64Encode(utf8.encode('$secretKey:'))}',
'Content-Type': 'application/json',
};
final body = {
"paymentKey": paymentKey,
"orderId": orderId,
"amount": amount.round(), // ✅ ensure integer for KRW
};
debugPrint("Confirm Request: $body");
final response = await http.post(
Uri.parse(apiUrl),
headers: headers,
body: jsonEncode(body),
);
debugPrint("Confirm Response: ${response.body}");
if (response.statusCode == 200) {
final responseData = jsonDecode(response.body);
return {'status': true, 'data': responseData};
} else {
final responseData = jsonDecode(response.body);
return {
'status': false,
'data': {
'code': responseData['code'],
'message': responseData['message'],
}
};
}
} catch (e) {
return {'status': false, 'data': e.toString()};
}
}