Guest API WebSocket disconnects on message send without widget

NICE CXone API & Integrations
1

Hey folks.

We are building a custom web messaging interface in C# backend with a vanilla JS frontend, completely bypassing the standard Messenger widget. The goal is to use the Guest API directly for a cleaner UI. Authentication works fine using the /api/v2/conversations/webmessaging/guests endpoint to get the guestToken and conversationId.

The connection to the WebSocket endpoint wss://api.mypurecloud.com/api/v2/conversations/webmessaging/guests/{guestId}/events establishes successfully. I receive the initial connection event. However, when I try to send a message via the HTTP POST to /api/v2/conversations/webmessaging/guests/{guestId}/conversations/{conversationId}/messages, I get a 200 OK response with the message object.

The problem is the WebSocket immediately drops with a close code 1006. No error payload. If I don’t send a message, the socket stays open for hours. Here is the payload I am sending:

{
 "content": "Hello from custom client"
}

Is there a specific header or sequence required? The docs are thin on this. I’ve tried adding the X-Genesys-Application header but it didn’t help. The socket dies every time. Any ideas?

2

The disconnect usually happens because the guest token expires or the handshake payload is malformed. You can’t just open the socket and fire text messages. The protocol expects specific JSON envelopes.

Here is the sequence that actually sticks. First, ensure you are sending the connect event immediately after the socket opens. The guestToken from the REST call is only valid for a short window, so don’t cache it.

const ws = new WebSocket(`wss://api.mypurecloud.com/api/v2/conversations/webmessaging/guests/${guestId}/connect`);

ws.onopen = () => {
 // Mandatory handshake
 const connectPayload = {
 type: "connect",
 data: {
 version: "1.0",
 supportedFeatures: []
 }
 };
 ws.send(JSON.stringify(connectPayload));
};

ws.onmessage = (event) => {
 const msg = JSON.parse(event.data);
 if (msg.type === "connect") {
 // Connection established. Now send actual message
 const chatPayload = {
 type: "message",
 data: {
 id: generateUUID(), // Must be unique
 conversationId: conversationId,
 text: "Hello world",
 timestamp: new Date().toISOString()
 }
 };
 ws.send(JSON.stringify(chatPayload));
 }
};

Check the onerror callback. If the server drops you right on send, it’s likely the conversationId doesn’t match the guestId context. They have to be paired correctly from the initial REST call. If you are using C# backend, make sure you are not URL-encoding the payload before sending over the socket. It breaks the parser.