Proactive web messaging notifications to previous guests

Is it possible to send a proactive notification to a customer who previously had a web messaging session?

Background

We’re trying to re-engage users after their session times out. The docs state, “Proactive messages can be sent to any guest with an active session ID.”

Issue

When I hit POST /api/v2/conversations/messaging/... with the old session ID, I get a 400 Bad Request. The payload looks correct based on the swagger spec.

Troubleshooting

I’ve verified the OAuth token has the webmessaging:guest:write scope. The session ID is definitely from a completed session. Not sure if the API supports cold outreach on closed sessions or if i’m missing a flag.