Short answer
HubSpot's KB: the integration connects to one GoToWebinar account. Sync past webinars manually and turn on auto-sync for new ones. The event's sync must be on to enroll contacts. It doesn't add personalized join links to HubSpot emails automatically.
1. In HubSpot
The relevant screen in my demo portal.

2. Worth knowing
Keep the GoToWebinar required fields to the set the KB lists, or registrations can fail.
3. Related
Zoom webinars and marketing events.