I put Odoo server on the internet... for example abc.com

I put PosBox on my local network (192.168.10.120)

I install pptp server on server abc.com with IP 192.168.30.1

I install pptp client on PosBox to connect to abc.com with IP 192.168.30.230

I can successfully PING each other between Odoo server and Posbox. And have set the Masquerade on the Odoo server network. If I connect the VPN on windows, I can browse the internet using the VPN IP Address.. so I can say the VPN server is running normally. I have set the IP for the printer proxy IP is 192.168.30.230

But when I run Point Of Sales, seems the printer still not found. Any idea to solve this?