I have checked all the firewall settings for the mentioned POS machines, I confirm that all of them have the proper access through the firewall but still they cannot reach internet.
I ran trace route command to check at what location in the network the internet access is blocked,
As shown below, the traffic stops at 10.77.31.1 which is located in our local network.
Please check why the network traffic stops at 10.77.31.1 which is under your administration.