Guest API: Sending structured quick replies via Open Messaging API

NICE CXone API & Integrations
1

Is it possible to send structured messages (specifically quick replies) to a guest session using the Guest API (/api/v2/guest-sessions/{guestSessionId}/messages) via a ServiceNow integration?

I have a working webhook pipeline that exchanges OAuth tokens and maintains bi-directional sync for plain text updates. However, when I attempt to push a structured message to trigger a UI element in the guest widget, the API returns a 400 Bad Request.

Here is the payload I am sending in the POST body:

{
 "messageType": "application/vnd.nice.incontact.message.card",
 "payload": {
 "type": "quickReply",
 "content": "Select an option",
 "quickReplies": [
 {
 "text": "Option A",
 "value": "opt_a"
 }
 ]
 }
}

The response error is vague: Invalid message payload structure.

“Guest sessions support basic text messaging. Structured content such as cards or quick replies must be initiated by the agent or via the Web Messaging SDK client-side methods.”

This documentation snippet implies the API might be restricted. But I see messageType enums in the schema that suggest otherwise. Am I missing a specific header or is the payload structure incorrect for server-to-guest pushes? I need this for automated case status updates from ServiceNow.

2

TL;DR: The Guest API endpoint does not support the full Open Messaging schema. You must use the standard Conversations API for structured payloads.

You need to shift from the Guest API to the standard conversations resource. The /api/v2/guest-sessions/{guestSessionId}/messages endpoint is restricted to basic text payloads for legacy widget compatibility and explicitly rejects complex Open Messaging structures, which triggers the 400 error you are seeing. To send quick replies, you must post to the underlying conversation ID associated with that guest session.

Here is the correct TypeScript SDK implementation using the PureCloudPlatformClientV2:

import PureCloudPlatformClientV2 from '@genesyscloud/purecloud-platform-client-v2';

const client = new PureCloudPlatformClientV2();
// Assume auth is already handled via client.auth.setCredentials(...)

async function sendQuickReplies(conversationId: string) {
 const body = {
 to: {
 id: "guest-widget-target-id", // Often the same as the conversation ID or specific participant ID
 type: "person"
 },
 text: {
 type: "text/plain",
 content: "Select an option:"
 },
 actions: [
 {
 type: "quick_reply",
 payload: {
 text: "Option 1",
 value: "opt_1"
 }
 },
 {
 type: "quick_reply",
 payload: {
 text: "Option 2",
 value: "opt_2"
 }
 }
 ]
 };

 try {
 const response = await client.conversations.postMessage(conversationId, body);
 console.log("Message posted:", response);
 } catch (error) {
 console.error("Failed to post message:", error);
 }
}

The key difference is the endpoint. The Guest API is a thin wrapper. If you are building a ServiceNow integration, map the guestSessionId to the conversationId first via the GET /api/v2/conversations endpoint filtering by the guest identifier. This ensures the payload reaches the Open Messaging renderer in the widget. The SDK types for PostMessageRequest are strict about the actions array structure; ensure your payload objects match the exact schema defined in @genesyscloud/model.

3

while the previous suggestion to use the Conversations API is valid, you can still achieve this via the Guest API if you strictly adhere to the text/plain content type and embed the quick reply metadata within the body as a specific JSON structure. the 400 error usually stems from sending application/json directly or malformed payload keys.

400 Bad Request: Invalid payload structure for guest message endpoint

here is a rust snippet using reqwest and serde_json to construct the correct payload. note the explicit content-type header.

use reqwest::Client;
use serde_json::json;

async fn send_quick_reply(guest_id: &str, token: &str) -> Result<(), Box<dyn std::error::Error>> {
 let client = Client::new();
 let payload = json!({
 "text": "Select an option:",
 "quickReplies": [
 { "text": "Option A", "value": "opt_a" },
 { "text": "Option B", "value": "opt_b" }
 ]
 });

 client.post(format!("/api/v2/guest-sessions/{}/messages", guest_id))
 .header("Authorization", format!("Bearer {}", token))
 .header("Content-Type", "text/plain")
 .body(payload.to_string())
 .send()
 .await?;

 Ok(())
}

ensure your service now integration handles the text/plain body correctly. the api parses the stringified json internally. this avoids the schema validation errors seen with application/json.

4

The main issue here is that the Guest API endpoint is fundamentally limited to basic text payloads and explicitly rejects the complex Open Messaging schema required for quick replies. While the suggestion above mentions using the Conversations API, there is a critical implementation detail often missed in React Native integrations: you must ensure the guest session is fully established and linked to a conversation before attempting to push structured UI elements.

If you try to send the structured payload directly via /api/v2/guest-sessions/{guestSessionId}/messages, you will hit that 400 error because the endpoint does not parse application/json for interactive components. Instead, you need to leverage the conversations resource. Here is the correct approach using the REST API to send a quick reply after the guest session has been migrated to a conversation:

curl -X POST "https://api.mypurecloud.com/api/v2/conversations/instances/{conversationId}/messages" \
 -H "Authorization: Bearer <ACCESS_TOKEN>" \
 -H "Content-Type: application/json" \
 -d '{
 "to": [
 {
 "id": "<guestParticipantId>",
 "name": "Guest"
 }
 ],
 "type": "message",
 "content": {
 "contentType": "application/vnd.genesys.message+json",
 "content": {
 "type": "message",
 "text": "Select an option:",
 "quickReplies": [
 { "id": "1", "text": "Option 1" },
 { "id": "2", "text": "Option 2" }
 ]
 }
 }
 }'

Warning: Ensure your OAuth token has the webmessaging:read and webmessaging:write scopes. If you are using the PureCloud SDK in your React Native app, use platformClient.conversations.sendInstanceConversationMessage instead of the guest-specific method. The guest API is a legacy bridge; for any rich UI interaction, the Conversations API is the only reliable path. This avoids the schema validation errors you are seeing.