Notification API WebSocket subscription failing with 403 after auth

NICE CXone API & Integrations
1

Trying to establish a WebSocket connection to wss://api.genesys.cloud/v2/websocket using the NotificationApi client in Kotlin.

Getting a 403 Forbidden immediately after sending the subscribe message with the conversation:messages event type.

val request = SubscribeRequest()
request.events = listOf("conversation:messages")
request.conversationIds = listOf(conversationId)
client.subscribe(request)

Auth token is valid and works for REST calls. Missing something in the handshake payload?