CORS preflight failure on Genesys Cloud Messenger widget in Next.js SSR environment

NICE CXone API & Integrations
1

Can anyone clarify the correct CORS configuration for the Genesys Cloud Web Messaging Guest API when deployed within a React Next.js application using Server-Side Rendering?

I am attempting to embed the Messenger widget into a Next.js 14 app. The application uses the standard OAuth 2.0 client credentials flow to obtain an access token via HashiCorp Vault, which I then pass to the widget initialization. The token generation works perfectly, and the scope includes webchat:read and webchat:write. However, when the client-side hydration occurs, the browser blocks the initial handshake request to /api/v2/conversations/webchat with a CORS error.

The specific error in the console is:
Access to fetch at 'https://api.mypurecloud.com/api/v2/conversations/webchat' from origin 'https://myapp.example.com' has been blocked by CORS policy: Response to preflight request doesn't pass access control check: No 'Access-Control-Allow-Origin' header is present on the requested resource.

I have verified that my Next.js middleware correctly sets the Access-Control-Allow-Origin header for my domain. I assumed the Genesys Cloud API would handle the rest, but it seems the preflight OPTIONS request is failing.

Here is my current widget configuration YAML:

widget:
 appId: "abc-123-def-456"
 origin: "https://myapp.example.com"
 tokenProvider: "dynamic" # Injected via props
 locale: "en-US"
 theme: "light"

I have tried the following:

  1. Adding https://myapp.example.com to the allowed origins in the Genesys Cloud organization settings.
  2. Using the genesys-cloud-messenger npm package instead of the script tag, but the underlying fetch call still fails.
  3. Checking the Network tab; the OPTIONS request returns a 403 Forbidden from the Genesys Cloud edge, not a 200 OK with CORS headers.

Is there a specific header I need to append to the preflight request, or is this a known limitation with SSR frameworks where the initial token injection happens server-side but the widget hydration happens client-side? I need to ensure the secret rotation logic in Vault doesn’t interfere with the widget’s internal token refresh mechanism.