Web Messaging Guest API: Typing indicators returning 404

Trying to send typing indicators via the Guest API. The docs say POST /api/v2/webmessaging/guests/{guestId}/typing should work, but I’m getting a 404 Not Found. The guest token is valid since I can send messages fine. Is this endpoint deprecated or am I missing a header? Here’s the payload:

{
 "conversationId": "conv-123"
}

Curl returns 404 immediately.