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Form Tester Fails to Load Due to CORS Configuration

Error message (sample)

Browser console messages indicating CORS/preflight failures. Example (redacted):

Preflight response is not successful. Status code: 400

Fetch API cannot load https://<portal-backend>/demapi/dem/demrender due to access control checks.

Access to fetch at 'https://<portal-backend>/demapi/dem/demrender' from origin 'https://preview.processfactorial.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.

Symptoms

  • The Form Tester page fails to load or cannot communicate with backend services.
  • Console shows CORS/preflight errors.

Scope

This issue can occur on Customer Hosted Model installations.

Known instances

Form Tester Access

When a user navigates to the ProcessFactorial Form Tester, the application may fail to load or be unable to communicate with the backend services.

Root cause

Cross-Origin Resource Sharing (CORS) restrictions on the portal backend Function App—specifically the Form Tester URL is not allowed in the backend Function App's CORS configuration.

Resolution

  1. Navigate to the portal backend Function App in the appropriate resource group in the Azure Portal.
  2. In the left-hand navigation panel, select CORS under the API section.
  3. Add the Form Tester URL (https://preview.processfactorial.com) to the list of allowed origins.
  4. Click Save to apply the changes.

Verification checklist

  • [ ] Form Tester loads without CORS errors in console
  • [ ] Backend requests from Form Tester succeed (200)