40040 — feature_not_enabled

The client subscribed to a room feature that is off: occupancy, presence, or raw message reactions (enableEvents: false or rawMessageReactions: false). Not terminal.

At a glance — HTTP 400 · terminal: no.

What to do

• Turn the room option on, or skip the subscribe on clients that do not need it.
• REST get() still works with the feature off — only the realtime subscribe is refused.
• Check the room options before mounting the feature's UI so the subscribe never fires in the first place.