Step 1: Delete cached files, images and cookies of web browser.
If spacedesk HTML5 VIEWER web page doesn’t load the latest version 0.9.10, just delete the cached files, images and cookies on browsers settings.
Step 2: check if the web browser supports websockets.
If the spacedesk HTML5 VIEWER is unable to connect, check the version of the web browser and make sure that it is updated.
If the secondary machine is a smartphone or tablet device the browser and OS needs to be most recent versions supporting websockets.
Just go to https://websocketstest.com/ to verify.