Thanks!
Yes, I use Photon! I think I'm on a very old, low-tier paid plan so it is super cheap. I was optimistic when I added multiplayer and wanted the additional capacity in case a bunch of people wanted to play but I forgot to turn it off.
I have updated the game description with additional info as you requested.
Making the diagonals a win condition are something I've thought about, along with other rule modifiers. However my full-time job takes all my time these days. Maybe I'll get back to bigger updates in the future.