Multiplayer connection problems

I'm currently working a single servre multiplayer games and I'm having some troubles that are starting to make it not worth it. When people try to connect, sometimes it will say they joined the room successfully on the client side but on the server side there are no problems. This does not always happen for everyone however. Some people can connect in Chrome and not Firefox, others can connect in either, and then some people can not connect in any browser. It also seems to be consistent with who cannot connect or can connect with certain methods. The people who can't connect anywhere won't ever be able to connect. The ones who don't have troubles will never have any troubles. Is this a problem on my end, and is there any way to fix it if it is?

Peer-to-peer connections are blocked by some firewalls or network setups. You will only get about 90% connectivity by default.

Ashley So is there a way for me to combat this on my end, or suggest to other users if they are unable to connect?

You could set up a TURN server, but then you have to pay for the server and the bandwidth that routes through it.

Note this is a problem of the architecture of the IPv4 internet - it's not specific to C2, any peer-to-peer connections have to deal with this.

Ashley So I take it that those people who can't connect at all will never be able to try out my game? That's pretty unfortunate considering it seems like a lot less than 90% are able to connect.

They can if they make the necessary adjustments to their network configuration, but that depends entirely on their specific setup.