Reaction received event

Fired when a participant adds or removes an emoji reaction on a message. Supported on WhatsApp, Telegram, Slack, Instagram and Facebook Messenger. Distinct from message.received so a reaction (e.g. a thumbs-up) is not mistaken for an inbound message. The reaction.action field is added or removed. On WhatsApp and Meta removals the platform does not report which emoji was removed, so reaction.emoji may be an empty string. Instagram and Facebook accounts connected before reactions shipped only emit this event after their webhook subscription is refreshed; reconnect the account if reactions never arrive. Requires the Inbox add-on.