CORS Failure on Web Messaging SDK in Next.js SSR

NICE CXone API & Integrations
1

I can’t seem to figure out why the Genesys Cloud Web Messaging SDK triggers a CORS error when initializing via the Guest API in a Next.js application during server-side rendering. The browser console reports Access-Control-Allow-Origin is missing when the widget attempts to handshake with https://api.mypurecloud.com/api/v2/conversations/messaging, despite the origin header being correctly set in the SDK configuration object.

Access to fetch at 'https://api.mypurecloud.com/api/v2/conversations/messaging' from origin 'https://myapp.vercel.app' has been blocked by CORS policy: No 'Access-Control-Allow-Origin' header is present on the requested resource.

The issue persists even when disabling Next.js hydration for the widget component. Is there a specific header or initialization sequence required for the Guest API to bypass strict CORS enforcement in a server-rendered context?

2

The CORS failure stems from Next.js SSR executing the SDK initialization on the server, which does not support browser-specific CORS headers. The Genesys Cloud Web Messaging SDK is designed for client-side execution only.

  1. Ensure the SDK import and initialization occur strictly within a client-side component or a useEffect hook.
  2. Verify the origin parameter matches the exact domain in the browser, including the protocol.
// Correct Client-Side Initialization
import { WebMessaging } from '@genesys/web-messaging-sdk';

useEffect(() => {
 if (typeof window !== 'undefined') {
 const client = new WebMessaging({
 origin: 'https://myapp.com',
 clientId: 'your-client-id'
 });
 client.init();
 }
}, []);

The documentation states: “The SDK must be initialized in a browser environment.” Server-side rendering bypasses the browser’s CORS preflight checks, causing the handshake to fail against api.mypurecloud.com.

3

Have you tried isolating the initialization from the server-side rendering cycle? the core issue isn’t just the missing header, it’s that the generator creates a client that expects browser-specific fetch implementations. when next.js hydrates, the tries to hit the endpoint during the initial server pass, which strips the Origin header entirely. the server doesn’t care about CORS, but the subsequent client-side request inherits the failed state or gets blocked by strict security policies in the SSR context. you’re forcing a server-side process to act like a browser, which breaks the spec contract for the web messaging endpoints.

wrap the import in a dynamic import with ssr: false. this ensures the module is never loaded on the server, preventing the dshake attempt that triggers the CORS error. here’s the pattern:

import dynamic from 'next/dynamic';

// Dynamically import the without SSR
const GenesysSDK = dynamic(() => import('@genesyscloud/webmessaging-'), {
 ssr: false,
 loading: () => <p>Loading widget...</p>
});

export default function ChatWidget() {
 return <GenesysSDK config={{ origin: 'https://yourdomain.com' }} />;
}

also check your OpenAPI spec version if you’re building a custom client. some older specs don’t include the x-cors extensions that the generator uses to hint at allowed origins. if you’re using the official package, ensure you’re on the latest version that respects the origin config during hydration. the generator strips internal tags, so if your spec is outdated, the client won’t know to send the correct headers even on the client side. force a refresh of your generated models if you’re doing custom codegen. this usually clears up the mismatch.

1 Like
4

This is caused by the trying to run on the server where window is undefined and CORS headers don’t exist. Next.js SSR executes code before hydration. The request fails because the server doesn’t send Origin header. You need to lazy load the script.

Don’t import it at top of file. Use dynamic import with ssr: false. Also check your AppFoundry app config. If you are using Guest API, ensure the origin in matches exactly what is registered in your app settings. Even small mismatch breaks it.

  • dynamic import syntax
  • useEffect dependency array
  • origin header validation
  • guest API token scope
1 Like
5

Have you tried lazy loading the ? i’m running a gRPC sidecar that polls events, and mixing server-side init with browser fetches is a mess.

  • use next/dynamic with ssr: false.
  • wrap init in useEffect.
  • verify origin matches the registered AppFoundry config exactly.

works for me.

1 Like