Open Routers with Authentications?

Hi everyone! This is my ever first post in there, so if there is any problem i'm so sorry, i'm a newbie on wonderhowto!

So without any furthers do, let's go into it.

Since i'm living where i am now, nearby there's an open router, without any pw in it, but once you're in the router page (192.168.8.1), it asks you to buy a limited period of time where you can use internet freely, logging in with your email account. I mean if you spend 30 euros, they would give you unlimited internet data for 30 days. The thing is that ever since i started using it, i can't port forward, i can't even do metasploit stuff in lan.. i believe it's just because even if i'm in lan and with my other pc connected in the same account in the router, they're not in the same gateway.. because of the authentication.. i don't really get this thing. Or maybe it's a router's firewall that doesn't allow me to, i don't really know! Oh and just clearing you out, i tried to ping with nmap the devices connected but nothing comes up, just the gateway and this pc.. could it be as i said? That even if my other pc is in the same network, it has a different gateway? And how can i solve that?

Thank you for the attention pals!! :D