Proactive Web Messaging Notifications for Past Guests via Guest API

Quick question about triggering proactive web messaging notifications for past guests. While my gRPC service reliably ingests web messaging webhooks, pushing a follow-up via the Guest API fails. A simple POST to the inbound open message endpoint carrying {"toId": "guest_123"} immediately yields 403 Forbidden.

  1. Extract guestId from inbound payload.
  2. Authenticate endpoint call with service token.
  3. Observe 403 Forbidden.
    Which Web Messaging SDK function handles re-engagement for expired sessions?
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