Node.js - process.env.computername is undefined, how to distinguish every device in same network?

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Node.js

Heroku

Express

I am writing a Node.Js server, I uploaded it to Heroku,
I'm using IPs to make a temporary cart for each user (device),
I want to distinct also every device in the same network,
I mean I want to make a cart for every user, (also in the same IP)
I tried to use mac address but it's getting the host mac address(the Heroku mac address).
I need the local device mac address

What I have tried:

let ip;
let ipAddr = req.headers['x-forwarded-for'];
if (ipAddr) {
  var list = ipAddr.split(",");
  ip = list[list.length - 1];
} else {
  ip = req.socket.remoteAddress;
}

const ipFoundOrNot = await IP.findOne({ postIP: ip });

IP is my Model Schema, I want to find also a computer name or something else better to distinguish also users in the same network,
I mean by that something like this...

let computerName = process.env.COMPUTERNAME;

const ipFoundOrNot = await IP.findOne({ postIP: ip,computerName:computerName });

But when I do process.env.COMPUTERNAME I get undefined in node js in heroku...
I also tried to get the device mac address, it works fine in localhost, But when I apply it to heroku, it's getting the mac address of the heroku server..