The code you have posted, is the code that creates a Webhook request, which you say you are getting a 202 so it is working successfully.
Where is your code handling your inbound callback requests?
You should have code that opens expects a HTTP GET to your callback of https://thehighlighthub.com/SubscribeTwitch that looks for a query string argument of hub.challenge and just echo that out with a 200 status code