If your Swagger UI is not visible when hosting your project on an IIS server, there are a few potential reasons and steps you can take to troubleshoot the issue:

1. Ensure Swagger is properly configured: Verify that you have properly configured Swagger in your project. Make sure you have installed the necessary NuGet packages and that you have the appropriate Swagger-related code in your startup configuration.
2. Check IIS configuration: Confirm that your IIS server is properly configured to serve the Swagger UI. Ensure that you have set up the correct bindings, application pool, and website configuration in IIS. Additionally, check that the necessary modules and handlers are enabled in IIS for Swagger.
3. Verify URL path and routing: Ensure that the URL path to access the Swagger UI is correct and matches the configured route in your application. Double-check the routing configuration in your project to make sure it’s properly mapped to the Swagger endpoint.
4. Check file and folder permissions: Verify that the necessary files and folders related to Swagger have appropriate permissions set. Ensure that the IIS process has read access to the Swagger files and the necessary folders.
5. Check for conflicting routes or middleware: Make sure there are no conflicting routes or middleware configurations that may interfere with accessing the Swagger UI. Check for any custom routes or middleware that may be blocking or redirecting the Swagger endpoint.
6. Enable detailed error messages: Enable detailed error messages in your IIS server to see if there are any specific error messages or exceptions related to the Swagger UI. This can provide additional information to help diagnose the issue.
7. Test locally and debug: Test your project locally with IIS Express or a local IIS server to see if the Swagger UI is accessible. Use debugging tools to identify any potential issues or exceptions that may be occurring during the request to the Swagger endpoint.

By following these steps, you should be able to troubleshoot and identify the cause of the Swagger UI not being visible when hosting your project on an IIS server.