Referral received event

Fired when someone opens an EXISTING Instagram or Messenger thread through an attributable entry point - an ig.me / m.me link with a ref parameter, or (Messenger) a returning Click-to-Message ad click - which Meta delivers as a standalone referral with no message attached. A referral that rides an inbound message (first message of a thread, icebreaker taps, returning ad clicks on Instagram) arrives on message.received under metadata.referral instead; the two never fire for the same click. The first referral captured on a conversation is also persisted on it (see metadata on GET /v1/inbox/conversations). Requires the Inbox add-on.