I am experiencing an issue with a Google Apps Script web app I developed. Despite following standard procedures, the app fails to load specific HTML pages based on URL query parameters. Here are the details:
Issue Description
Problem: The web app does not navigate to different pages (such as ‘index’, ’employee’, ‘admin’) based on the URL query parameter page. The URL does not change, and I receive an error message instead of the expected content.
Error Message: “Sorry, unable to open the file at this time. Please check the address and try again.
Steps Taken
Project Setup:

The project includes index, employee, and admin HTML files, referenced without the .html extension in the code.
A doGet function handles URL query parameters to determine which HTML file to serve:

Testing and Debugging:
Verified that file names are correct and match the references in the code.
Checked browser cache and tested in incognito mode to rule out caching issues.
Ensured proper deployment and public access settings.
Monitored network requests and console logs for errors.
Issue Persistence:
The problem persists with minimal HTML content and correct setup.
URLs used include parameters like ?page=admin, but the app does not navigate to the correct page.
Additional Context
Deployment URL: [Your Deployment URL]
Attempts: Multiple re-deployments, browser tests, and code simplifications have been tried without success.
Request
Could you please assist in diagnosing the issue? Are there any known issues with handling URL parameters in Google Apps Script web apps or potential configurations I might be missing? Any guidance or additional steps to resolve this would be greatly appreciated.

Thank you for your assistance.