This feature is available in Catalyst, Enterprise, and Ultimate editions.
Also, verify that the following have taken place:
The repository was correctly added in the CommitStream Administration page.
The associated webhook URL has been placed in the relevant repository inside your version control system (see How do I add webhooks in common version control systems?)
The commit comment contains a mention of the workitem ID you are committing against (i.e. S-12345 or B-12345)
See to Using CommitStream for more information.