Error while running slack-web api and express server - node.js

Question

I am trying to integrate WhatsApp and Slack for developing a chatbot. I am using WATI as my WhatsApp API provider and Slack Web API in Node.js
For testing locally I am ngrok to generate a webhook URL. But I am unable to receive WhatsApp incoming messages as it gives the following error:
process.nextTick(function () { throw userError; });
Error: Slack request signing verification failed
server.js
require('dotenv').config('/.env')
const express = require("express")
const app = express()
const PORT = process.env.PORT || 8000
const token = process.env.SLACK_BOT_TOKEN
const eventsApi = require('#slack/events-api')
const slackEvents = eventsApi.createEventAdapter(process.env.SLACK_SIGNING_SECRET)
const { WebClient, LogLevel } = require("#slack/web-api");
const client = new WebClient(token, {
logLevel: LogLevel.DEBUG
});
app.use('/', slackEvents.expressMiddleware())
//Route for WhatsApp
app.post('/wa-slack', async (req, res) => {
console.log(req)
});
slackEvents.on("message", async (event) => {
console.log(event)
// if (!event.subtype && !event.bot_id)
// client.chat.postMessage({
// token,
// channel: event.channel,
// thread_ts: event.ts,
// text: "Hello World!"
// })
})
app.listen(PORT, () => {
console.log(`App listening at http://localhost:${PORT}`)
})
The signing secret for slack is correct because the server runs successfully if I remove the following block
app.post('/wa-slack', async (req, res) => {
console.log(req)
});
Is there a way I can use the express server for handling both Slack and WhatsApp incoming requests?
Or do I need to create separate servers?
Any help or advice is appreciated, Thank you!