The channel_shared event is sent to all event subscriptions when a new shared channel is created or a channel is converted into a shared channel. It's also triggered when an external workspace is added to an existing shared channel.
The connected_team_id value is the team ID of the workspace that has joined the channel. Note that this ID may start with E, indicating that it is the ID of the organization that has been removed from the channel.
The channel value is the ID for the public or private channel.
This event is supported as a bot user subscription in the Events API. Workspace event subscriptions are also available for tokens holding at least one of the channels:read or groups:read scopes. Which events your app will receive depends on the scopes and their context. For instance, you'll only receive channel_shared events for private channels if your app has the groups:read permission.