Guest API 403 when sending message via Node.js script

Getting a 403 Forbidden when hitting POST /api/v2/conversations/messaging/ from a Node.js script. I’m trying to send messages without the widget to sync with our WFM adherence logs. The OAuth token works fine for GET requests. Here is the payload:

{
 "to": [{"id": "12345", "type": "user"}],
 "text": "Test"
}

The response says guestAccessEnabled is false, but it’s enabled in the org settings. Is there a specific scope I’m missing for the token?