我尝试在flutter应用中使用stripe_payment包实现Stripe支付系统，在代码中调用了Stripe.instance.initPaymentSheet（...），但是当我在几行代码之后尝试调用Stripe.instance.presentPaymentSheet（...）时，我得到了这个错误：

flutter: StripeException(error: LocalizedErrorMessage(code: FailureCode.Failed, localizedMessage: No payment sheet has been initialized yet, message: No payment sheet has been initialized yet, stripeErrorCode: null, declineCode: null, type: null))

下面是我的代码：

Future<void> makePayment() async {
    final url = Uri.parse(
        '${firebaseFunction}');

    final response =
        await http.get(url, headers: {'Content-Type': 'application/json'});

    this.paymentIntentData = json.decode(response.body);

    await Stripe.instance.initPaymentSheet(
        paymentSheetParameters: SetupPaymentSheetParameters(
            paymentIntentClientSecret: paymentIntentData!['paymentIntent'],
            applePay: true,
            googlePay: true,
            style: ThemeMode.dark,
            merchantCountryCode: 'UK',
            merchantDisplayName: 'Test Payment Service'));
    setState(() {});

    print('initialised');
    try {
      await Stripe.instance.presentPaymentSheet();
      setState(() {
        paymentIntentData = null;
      });
      ScaffoldMessenger.of(context).showSnackBar(SnackBar(
        content: Text('Payment Successful!'),
      ));
    } catch (e) {
      print(e);
    }
    // await displayPaymentSheet();
  }

下面是我的node.js代码（通过url访问）：

const functions = require("firebase-functions");

const stripe = require('stripe')(functions.config().stripe.testkey);

exports.stripePayment = functions.https.onRequest(async (req, res) => {
    const paymentIntent = await stripe.paymentIntents.create({
        amount: 170,
        currency: 'usd'
    },
    function(err, paymentIntent) {
        if (err != null) {
            console.log(err);
        } else {
            res.json({
                paymentIntent: paymentIntent.client_secret
            })
        }
    })
})

当我尝试使用presentPaymentSheet方法时，为什么Payment Sheet没有初始化（或保持初始化）？