Genesys Cloud Guest API WebSocket connection failing with 403 in Android

Trying to spin up a custom chat UI in Kotlin using the Guest API WebSocket endpoint at wss://{subdomain}.mypurecloud.com/api/v2/guest/conversations/websocket. The connection attempt immediately returns a 403 Forbidden. I’m passing the guestId and conversationId in the initial JSON payload as shown in the docs.

{"action": "connect", "guestId": "abc-123", "conversationId": "def-456"}

Is there a specific header or auth token required for this endpoint that isn’t documented, or is the guestId format wrong?