You can use the Get Webhook Subscriptions endpoint to see if a subscription is live https://dev.twitch.tv/docs/api/reference#get-webhook-subscriptions
Also, you don’t appear to have a POST handler so wont get any notifications as you have no way to handle incoming POST requests, so Twitch will repeatedly try to resend the notifications as you’re not responding to them.
Couple other things I noticed too, your subscribeHook function doesn’t actually seem to do anything, you just assign a few constants, you don’t actually resolve/reject the promise or actually do anything.
"accept": "application/vnd.twitchtv.v5+json" also doesn’t do anything at all in Helix, that’s a thing for v5, you shouldn’t be sending that for any Helix endpoints.