Getting 409 Conflict when trying to send proactive message to previous guest ID

Hey everyone,

We are trying to set up a simple re-engagement flow for our WFM team. The idea is to send a proactive notification to a customer who had a web messaging session with us yesterday, asking if they need further help. I’ve got the guest ID from the previous conversation.

I’m hitting the /api/v2/conversations/messaging/messages endpoint with a POST request. Here is the JSON payload I am sending:

{
 "to": {
 "id": "8a8b9c0d-7e6f-5a4b-3c2d-1e0f9a8b7c6d",
 "type": "guest"
 },
 "from": {
 "id": "my-bot-user-id",
 "type": "user"
 },
 "text": "Hi there, do you still need help with your order?"
}

The response I get back is a 409 Conflict. The error message says:

“Conversation not found or already ended.”

I checked the docs and it seems like you can’t just post to a closed conversation. But how do I send a proactive message to a guest who isn’t currently in an active session? Do I need to start a new conversation and somehow link it to the previous one, or is there a different endpoint I should be using for proactive outreach?

I feel like I’m missing a step here.