Starts a Real Time Messaging session.

Optional Params

• mpim_aware - Returns MPIMs to the client in the API response.
• no_unreads - Skip unread counts for each channel (improves performance).
• simple_latest - Return timestamp only for latest message object of each channel (improves performance).

Errors the API can return:

• migration_in_progress - Team is being migrated between servers. See the team_migration_started event documentation for details.