Guest API message send loop with 409 CONFLICT on concurrent sessions

NICE CXone API & Integrations
1

We are building a custom web messaging interface that bypasses the standard Messenger widget. The goal is to handle the entire conversation lifecycle using the Guest API endpoints directly from our frontend React app. The setup works fine for the initial message, but we run into issues when trying to send subsequent messages while the agent is typing or when there is any latency in the server response.

Here is the flow we have implemented:

  1. Create a guest user via POST /api/v2/conversations/guests.
  2. Start a conversation with POST /api/v2/conversations targeting a specific routing queue.
  3. Send the first message using POST /api/v2/conversations/{conversationId}/messages.

The problem occurs on step 3 for the second message. If we send a message before receiving the message-sent event or if the server is slow to process the previous one, we get a 409 CONFLICT error. The error message says Message version mismatch. We tried implementing a retry logic with exponential backoff, but it feels hacky and causes duplicate messages if the retry succeeds after the original was actually processed but the event was lost.

We are using the JavaScript SDK to manage the WebSocket connection for events, but we are making direct REST calls for sending messages because the SDK’s send method doesn’t seem to expose the version control details we need to debug this.

Here is the JSON payload we are sending for the second message:

{
 "to": [
 {
 "id": "agent-user-id-here",
 "type": "user"
 }
 ],
 "text": "Is this working now?",
 "version": 1
}

We assumed version increments automatically on the server, but it seems we need to track it client-side. The documentation is vague on how to handle this in a high-concurrency scenario. Are we supposed to poll for the latest version before sending? That seems inefficient.

Environment specs:

  • Genesys Cloud US-East
  • React 18 frontend
  • Guest API v2
  • Custom WebSocket listener for events

We need a reliable way to handle message versioning without blocking the UI or causing conflicts. Any code examples for proper version tracking would be appreciated.