Chat fundamentals
Contact subscription
Subscription and consent on the contact record, often viewed from Inbox.
Subscription state belongs to the contact, not an individual chat. You may view or update it from the Inbox contact card while handling a conversation, or change it for many contacts at once with the Subscribe / Unsubscribe bulk action — and you can filter the conversation list by subscription status with advanced filters or a saved view.
For what subscription means and how it affects journeys and messaging, see Contact subscription.