"Unable to parse Build/Web builds.framework.js.br! This can happen if build compression was enabled but web server hosting the content was misconfigured to not serve the file with HTTP Response Header "Content-Encoding: br" present. Check browser Console and Devtools Network tab to debug."
After this, I wanted to download it, but I was greeted with a paywall, so I stopped trying right there.
Update: I tried to give it another go and actually proceeded to download the game (I know you can download it without paying, but seeing the paying suggestion was discouraging). Controlling two players at the same time is quite hard. Also, Player 2's attack doesn't work, so the first wave of enemies is unbeatable.