Could you provide some more information? What browser are you using? Are you using a script blocker? (if so, make sure to disable it on *.hwcdn.net) Are you blocking third-party cookies? (if so, make sure to disable that on the same domain)
It works fine for me on the client. (you do need to click Start). The game will launch in your default web browser. If it still does not work, you can try just playing in your browser directly instead of via the client (https://flori9.itch.io/the-final-earth-2).
just use CoolMathGames to play it. the link to The Final Earth 2 is right there.