Please update your instance by downloading the latest WAR file from https://h-mdm.com/download/. Clear the browser cache, disable ad blockers if you're using them, and reload the page.
If you're using the reverse proxy in front of Headwind MDM, make sure they are not blocking any traffic (you can check that in the Chrome developer console, Network tab).
If the error persists, please contact us and provide the URL of your Headwind MDM instance.