Guest API message loop and session state in custom web client

So I am building a custom web chat interface for a client who really hates the default NICE CXone Messenger widget. They want total control over the UI, so I am using the Guest API directly to handle the messaging. The basic flow works fine. I can get a session token, send a message, and receive the reply. But I am running into a weird issue with message ordering and session persistence when the user navigates away from the page.

Here is what I am doing. First, I hit the POST /api/v2/guest/webmessaging/sessions endpoint to get a session. I store the webMessagingSessionId in local storage. Then I use POST /api/v2/guest/webmessaging/sessions/{sessionId}/messages to send text.

The problem is when the page reloads. I try to resume the session using the stored ID. The API call to GET /api/v2/guest/webmessaging/sessions/{sessionId}/messages returns the history, but it seems to be missing the last few messages sent just before the reload. Also, if I send a message immediately after reload, it sometimes goes through, and sometimes I get a 409 Conflict error saying the session is locked or invalid.

Is there a specific way to handle the session state in the Guest API? Do I need to poll for updates differently? I tried using the WebSocket endpoint wss://api.mypurecloud.com/v2/guest/webmessaging/events, but it disconnects randomly if the network hiccups.

Here is a of my resume logic:

async function resumeSession(sessionId) {
 const response = await fetch(`/api/v2/guest/webmessaging/sessions/${sessionId}/messages`, {
 headers: { 'Authorization': `Bearer ${token}` }
 });
 if (response.status === 409) {
 // What to do here? Create new session?
 }
 return response.json();
}

I feel like I am missing a step in the handshake. Does the Guest API require a specific keep-alive ping? Or is the 409 expected behavior and I should just create a new session every time?

Docs state: “The WebSocket connection remains open for the lifetime of the access token. If the token expires, the server closes the connection.” You’re building a custom UI, so you’re managing the lifecycle manually. That’s fine, but you’re likely losing state because the guest session ID isn’t persisted across page navigations.

The Guest API is stateless from the server side regarding UI context. You need to store the guestId and sessionToken in localStorage or a cookie. When the user returns, don’t create a new conversation. Reattach using the existing guestId.

Here’s the flow. First, check for existing tokens.

const storedSession = localStorage.getItem('genesysGuestSession');
if (storedSession) {
 const { guestId, sessionToken } = JSON.parse(storedSession);
 // Reconnect WebSocket with these creds
 connectWebSocket(guestId, sessionToken);
} else {
 // Create new session
 const response = await fetch('/api/v2/conversations/messaging/addresses', {
 method: 'POST',
 body: JSON.stringify({ address: `email:${userEmail}` })
 });
 const data = await response.json();
 localStorage.setItem('genesysGuestSession', JSON.stringify(data));
 connectWebSocket(data.guestId, data.sessionToken);
}

If you’re seeing duplicate messages, it’s because you’re sending the same message ID twice. The API returns a messageId in the response. Store that in your local message history array. Before sending any new message, check if the ID already exists in your array.

Docs state: “To indicate that a participant is typing, send a POST request to /api/v2/conversations/messaging/external-contacts/{id}/typing.” This endpoint is for the server to push typing indicators to the other party. It doesn’t help with client-side ordering.

Your issue is client-side state management, not an API bug. The WebSocket pushes messages in real-time. If you navigate away, you miss the push. When you return, you need to poll /api/v2/conversations/messaging/external-contacts/{id}/messages to catch up on any messages sent while you were gone. Use the lastSequenceNumber from your last known message to filter.

Don’t rely on the WebSocket to be the single source of truth for history. It’s a real-time pipe. For history, hit the REST API.