Set PHP cookie name with custom ids "attached" to it - php

Question

I'm trying to set a cookie for each profile which was seen by someone so that the custom welcome popup is not showing up everytime on return.
Now this happens with a specific profile and there the custom welcome popup is not showing, but if I'm going to another profile the custom welcome popup will not be showed too, which is something I don't want to happen.
That is why I need to set custom cookies in the users browser like : seen(here goes the id of the seller of smth else).
Doing this using PHP is not working:
When the user is closing the popup , I send an AJAX request with an ID payload to a specific file which sets the seen cookie. My AJAX request works all fine, but the cookie does not accept a specific id near its name. Should I work with the value of the cookie instead?
This is how my set cookie file looks like:
<?php
session_start();
$id = $_POST['id'];
setcookie("seen$id",true, time() + (86400 * 30), "/");
//seen$id is the custom cookie name
?>
Is it possible to set these type of cookies?
Chrome is showing up the name of the cookie (seen) without the ID near it.

Answer 1

This is not wise.
Unless you know that the set is bounded, then you have an undefined number of cookies, and hence an undefined amount of data which needs to be sent back to the server with each HTTP request. In practice, most browsers and web servers will limit either or both of the number of cookies and size of the data. While there is a case for using browser-sode data storage to address issues of scalability, that clearly does not apply here given that you are also using server-side sessions.
Going back to the problem you describe - your description is vague. It would have been helpful if you had shown us the actual Set-Cookie headers returned by the server.
The logic of your code is bad. While you might expect this URL to only ever see POST requests, and specifically POST requests with 'id' set, it is good practice to write robust code that does not rely on side effects elsewhere. While it is ALSO good practice to only provide the minimum code necessary to reproduce the issue when posting on StackOverflow, in this case the the effects you are reporting will only arise if the URL is invoked without 'id' or with a verb other than POST.
Consider:
<?php
session_start();
if (isset($_POST['id'])) {
$id = $_POST['id'];
setcookie("seen$id",true, time() + (86400 * 30), "/");
}