Webhook Error: Webhook payload must be provided as a string or a Buffer

I’m stuck on this, could someone help me?
I put it in postman: https://my-server/api/webhook

and i receive this:

Webhook Error: Webhook payload must be provided as a string or a
Buffer (https://nodejs.org/api/buffer.html) instance representing the
raw request body.Payload was provided as a parsed JavaScript object instead. Signature verification is impossible without access to the
original signed material.

Learn more about webhook signing and explore webhook integration
examples for various frameworks at
https://github.com/stripe/stripe-node#webhook-signing

i’m using ReactJS and Node

const express = require('express');
const Stripe = require('stripe');
const bodyParser = require('body-parser');
const cors = require('cors');
const webhookRoutes = require('./routes/webhook');

const app = express();
const stripe = Stripe(
  'sk_test_51Q1x2cRraDIE2N6qLbzeQgMBnW5xSG7gCB6W3tMxCfEWUz8p7vhjnjCAPXHkT2Kr50i6rgAC646BmqglaGWp5dhd00SZi9vWQg',
);

app.use(cors());
app.use(express.json());
app.use('/webhook', express.raw({ type: 'application/json' }));
app.use('/api', webhookRoutes);

app.post('/create-checkout-session', async (req, res) => {
  try {
    console.log('Received request to create checkout session');

    const session = await stripe.checkout.sessions.create({
      payment_method_types: ['card'],
      line_items: [
        {
          price_data: {
            currency: 'usd',
            product_data: {
              name: 'Nome do Produto',
            },
            unit_amount: 2000,
          },
          quantity: 1,
        },
      ],
      mode: 'payment',
      success_url: 'http://localhost:5173/success',
      cancel_url: 'http://localhost:5173/cancel',
    });

    console.log('Checkout session created successfully:', session);
    res.json({ id: session.id });
  } catch (error) {
    console.error('Error creating checkout session:', error.message);
    res.status(500).json({
      error: 'Failed to create checkout session',
    });
  }
});

const PORT = process.env.PORT || 4242;
app.listen(PORT, () => console.log(`Server running on port ${PORT}`));

const express = require('express');
const Stripe = require('stripe');
const router = express.Router();
const stripe = Stripe('sk_test');

router.post('/webhook', async (req, res) => {
  const sig = req.headers['stripe-signature'];

  let event;

  try {
    event = stripe.webhooks.constructEvent(req.body, sig, 'whsec_');
  } catch (err) {
    console.log(`Webhook Error: ${err.message}`);
    return res.status(400).send(`Webhook Error: ${err.message}`);
  }

  if (event.type === 'checkout.session.completed') {
    const session = event.data.object;

    console.log('Pagamento confirmado:', session);
  }

  res.json({ received: true });
});

module.exports = router;