Embedding the Genesys Cloud Messenger in a Next.js 14 app. Using App Router. The widget loads fine in dev, but on the production build (Vercel), the initial handshake fails.
The console throws:
Access to fetch at 'https://mypurecloud.ie/api/v2/externalMessaging/conversations' from origin 'https://myapp.com' has been blocked by CORS policy: No 'Access-Control-Allow-Origin' header is present on the requested resource.
I’ve checked the docs. They say:
“The Messenger SDK handles CORS headers automatically when configured correctly.”
My config:
const messengerConfig = {
organizationId: 'org-123',
deploymentId: 'dep-456',
onMessage: (msg) => console.log(msg)
};
useEffect(() => {
Messenger.init(messengerConfig);
}, []);
The request is going to the correct region endpoint. The token generation via client credentials works fine on our backend. But the browser fetch is blocked.
Is there a specific header I need to pass in the init options? Or is this a Next.js SSR hydration mismatch causing the origin check to fail before the SDK patches the headers?
The docs don’t mention Next.js specifically. Just standard SPA. This feels like a server-side rendering edge case.
The Messenger widget doesn’t hit your API directly. That fetch is coming from the Genesys Cloud edge, not your Next.js server. You’re looking at this wrong.
You’re likely hitting a scope mismatch on the OAuth token used by the widget config. The Messenger client needs messaging:write or messaging:read depending on your setup, but more importantly, it needs to be valid for the specific external messaging channel you’re targeting. If your token is scoped only to user:read, the API will reject the handshake before CORS even becomes the primary issue, though the browser masks it as a CORS error.
Check your window.genesyscloud.messenger.init config. Ensure the authToken isn’t expiring prematurely or lacking the correct division ID. Also, verify that your Next.js middleware isn’t stripping the Authorization header if you’re proxying anything. It’s easy to accidentally block legitimate headers in the edge runtime.
window.genesyscloud.messenger.init({
orgId: 'your-org-id',
deploymentId: 'your-deployment-id',
authToken: 'valid-oauth-token-with-messaging-scope',
// Ensure this matches your external messaging channel settings
});
Double-check the token scopes in the Admin console under Integrations > OAuth. Missing messaging:write is a common trap.