When you make a subscription request, the only response you will get is whether or not the subscription is successful.
To get the updates, you need to properly handle updates being sent by Twitch to the endpoint you have specified in hub.callback. You will only receive updates here once a subscription request succeeds, and only for the duration specified in hub.lease_seconds
We worked to conform closely to the W3 spec for webhooks https://w3c.github.io/websub/ Hopefully this can answer some of your questions.