2Hire Webhook URL Not Working in Express.js After Conversion from Fastify

I recently converted a Fastify application handling 2Hire webhooks to Express.js. However, the webhook URL isn't triggering as I expected.

2Hire webhooks Subscription API Doc: https://developer.2hire.io/reference/subscribe-1

2Hire webhooks Receiving signals Doc: https://developer.2hire.io/docs/receiving-signals

Error

{"message": {"code": "CHALLENGE_ERROR","errorId": "2c31cx-x-x-x-x82034a925","details": {"cause": "CHALLENGE_FAILED"        }    }}

Despite setting up the raw body correctly and configuring the endpoint, the webhook does not trigger when tested.

Can anyone help identify what might be going wrong or what I may have missed in the conversion?

Below is the core part of my implementation:

const express = require('express');const bodyParser = require('body-parser');const crypto = require('crypto');const dotenv = require('dotenv');dotenv.config();const app = express();const SECRET = process.env.SECRET;const PORT = 8080;const signalNames = new Set(["online", "position", "distance_covered", "autonomy_percentage", "autonomy_meters", "*"]);function isSignal(signal) {    return signalNames.has(signal);}function validateTopic(topic) {    const parts = topic.split(":");    return parts.length === 4 && parts[0] === "vehicle" && parts[2] === "generic" && isSignal(parts[3]);}function generateSignature(message, secret) {    const hmac = crypto.createHmac('sha256', secret);    hmac.update(message, 'utf8');    return `sha256=${hmac.digest('hex')}`;}app.use(bodyParser.json({    verify: (req, res, buf) => {        req.rawBody = buf.toString();    }}));app.get('/listener', (req, res) => {    const { 'hub.mode': mode, 'hub.topic': topic, 'hub.challenge': challenge } = req.query;    if (!validateTopic(topic) || mode !== 'subscribe') {        res.status(400).send('Validation error');    } else {        res.send(challenge);    }});app.post('/listener', (req, res) => {    const signature = req.headers['x-hub-signature'];    const computedSignature = generateSignature(req.rawBody, SECRET);    if (!validateTopic(req.body.topic) || signature !== computedSignature) {        res.status(401).send('Invalid signature or topic');    } else {        console.log("Webhook Received: ", req.body);        res.send('Webhook received');    }});app.listen(PORT, () => {    console.log(`Server listening on http://localhost:${PORT}`);});