That's interesting... tried clicking a few times in the game window in case it's a focus issue?
Beyond that, which browser? I exclusively tested in Chrome, though I've just checked IE11 and it worked fine after clicking the game window a couple of times.
Failing that, which O/S? It was made in GameMaker Studio 2 so I could export a native Windows or Linux build easily enough. Mac would be a bit more painful, but doable too.