Trying to bypass the Messenger widget entirely and post messages directly via the Guest API. The initial handshake works fine, but attempting to send a message to the session fails with a 400 Bad Request. Payload is standard JSON with text and from fields. No error details in the response body.
{
"text": "Hello",
"from": { "id": "guest-123" }
}
Missing something obvious in the auth header or session state?