Web Messaging SDK: Re-engaging a guest with a previous session ID

Trying to send a proactive notification to a customer who had a chat session yesterday. I’m using the @genesyscloud/web-messaging-sdk in a Node.js backend script. I have the guestId from the old session, but when I try to call createConversation with that ID, it just spins up a brand new guestId instead of re-attaching to the old one.

const conversation = await sdk.conversationsApi.createConversation({
 body: {
 guest: { id: oldGuestId },
 type: 'web'
 }
});

Is there a specific API endpoint to ‘wake up’ a dormant session?