Invalid transport

API
4

So what are you sending now?

				'transport': {
					'method': 'webhook',
					'callback': 'http://localhost:4256/webhooks/callback',
					'secret': clientSecret
				}

Should become, not the lack of a :443 as https defaults to 443 and specifying a port is likely the issue. Or the fact you are using your clientSecret as a shared secret.

				'transport': {
					'method': 'webhook',
					'callback': 'https://ngrokurl/webhooks/callback',
					'secret': randomString
				}

Also this is VERY IMPORTANT

DO NOT USE YOUR CLIENT SECRET AS THE TRANSPORT SECRET

Use a random string of stuff

See

The secret is a string between 10 and 100 characters that your application will define and send to Twitch in the subscription creation process. As a result, this secret should not be your Client Secret or Extension secret.

https://dev.twitch.tv/docs/eventsub