The method 'startPayment' isn't defined for the type 'PayUCheckoutProFlutter'

Question

in code The method 'startPayment' isn't defined for the type 'PayUCheckoutProFlutter'. Try correcting the name to the name of an existing method, or defining a method named 'startPayment'.

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

import 'package:payu_checkoutpro_flutter/payu_checkoutpro_flutter.dart';

class MyClass extends StatefulWidget {
  @override
  _MyClassState createState() => _MyClassState();
}

class _MyClassState extends State<MyClass> implements PayUCheckoutProProtocol {
  late PayUCheckoutProFlutter _checkoutPro;

  @override
  void initState() {
    super.initState();
    _checkoutPro = PayUCheckoutProFlutter(this);
  }

this method i use

 @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('PayU Checkout Pro'),
      ),
      body: Center(
        child: ElevatedButton(
          child: Text("Make Payment"),
          onPressed: () async {
            String orderId = DateTime.now().millisecondsSinceEpoch.toString();
            String amount = "1";

            var response = await _checkoutPro.startPayment( // here show this error in startPaymnet
              orderId: orderId,
              amount: amount,
              productInfo: 'iPhone 12',
              merchantKey: 'your_merchant_key',
              userPhoneNumber: '9999999999',
              transactionId: orderId,
              firstName: 'Orange',
              merchantSalt: 'your_merchant_salt',
              email: '[email protected]',
              hashUrl: '',
              userCredentials: '',
            );

            // Handle the response
            if (response['status'] == 'success') {
              handlePaymentSuccess(amount);
            } else if (response['status'] == 'failed') {
              handlePaymentFailure(amount, response['message']);
            }
          },
        ),
      ),
    );
  }

  @override
  generateHash(Map response) {
    // Implement the logic to generate the hash using the response received from your backend server
    // Pass the generated hash to the SDK using _checkoutPro.hashGenerated(hash: hashResponse);
    // Example:
    Map<String, String> hashResponse = {
      'hashName': 'paymentHash',
      'hash': 'your_generated_hash_here',
    };
    _checkoutPro.hashGenerated(hash: hashResponse);
  }

  @override
  onPaymentSuccess(dynamic response) {
    // Handle the payment success response
  }

  @override
  onPaymentFailure(dynamic response) {
    // Handle the payment failure response
  }

  @override
  onPaymentCancel(Map? response) {
    // Handle the payment cancel response
  }

  @override
  onError(Map? response) {
    // Handle the error response
  }

  void handlePaymentSuccess(String amount) {
    // Handle payment success logic
  }

  void handlePaymentFailure(String amount, String message) {
    // Handle payment failure logic
  }

how to slove this error whats a method for startPayment for call payment function. payu_checkoutpro_flutter depedancy use is right for payu payment gateway?