Backend close for Web Messaging Guest API

Trying to end a chat session from a server-side script using the Genesys Cloud JS SDK. The guest side is just a static widget, so the backend needs to handle the termination. I’ve got the conversationId and guestId from the webhook payload. Calling webMessagingApi.closeGuestConversation(conversationId) returns a 400 Bad Request. The error message says guestId is missing, but the SDK method signature for that endpoint doesn’t seem to accept it as a parameter. It just takes the ID. Here’s the call:

const res = await client.webMessagingApi.closeGuestConversation(conversationId);

Docs are sparse on the server-side closure flow. Is there a different endpoint or a PATCH method I should be hitting instead? The closeConversation method exists but that requires an agent ID, which we don’t have in this context since it’s unstaffed. Just need a way to kill the session programmatically without waiting for the TTL. The 400 response is blocking the cleanup job.