Could you add a bit about how you made the game? I’ve been interested in making .io games for some time.

I used Phaser + uWebSockets. Source code is public, feel free to take a look: https://github.com/codergautam/swordbattle.io

Nice! What's your tech stack here?

NodeJS, React, Postgres (for accounts), uWebSockets and Phaser

You make $500+/mo from that game?

Used to at least, still gets a lot of traffic mainly from web game portals but not promoting it rn.