Guest API POST /api/v2/conversations/messaging/contacts typing indicator returns 400

Trying to wire up typing indicators for the web messaging widget using the Guest API. The docs state: “To send a typing indicator, POST to /api/v2/conversations/messaging/contacts with a typing payload.” I’ve got the conversation ID and the contact ID from the initial handshake.

Here’s the payload I’m sending:

{
 "conversationId": "8f3a2b1c-9d4e-5f6a-7b8c-9d0e1f2a3b4c",
 "typing": true
}

The request returns a 400 Bad Request. The error body says: “Invalid payload structure.” I’m using the client credentials token I generated earlier for the bot user. Is the typing field supposed to be nested differently? Or do I need to use a different endpoint for read receipts? The documentation is pretty sparse on the exact JSON schema for these soft events.