If you haven’t already, you’ll need to play the sequence. You can choose “AutoPlay” on the level sequence actor to play it when the level loads. Or you can trigger it through blueprints:
https://docs.unrealengine.com/latest/INT/Engine/Sequencer/HowTo/TriggeringSequences/
Another possibility is that you need to create a camera cut track to bind your camera to the viewport:
https://docs.unrealengine.com/latest/INT/Engine/Sequencer/HowTo/TracksCameraCut/