TeamSpeak 3 PHP Framework

I am still learning PHP and it's the first time I am using this library (TeamSpeak 3 PHP Framework), I am trying to return a count of online users in a specific group, I tried a few different ways and no success.

This one, counts all users in the group (including offline users):

PHP Code:

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$admins = 0;
foreach($ts3->serverGroupGetById(12)->clientList() as $client) {
    $admins++;
} 


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So I tried to compare that list with the online users list:

PHP Code:

---

$admins = 0;
foreach($ts3->serverGroupGetById(12)->clientList() as $client) {
    if($ts3->clientList($client)) {
        $admins++;
    }
} 


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And it works sometimes, I say sometimes because I tried it on my virtual server and no issues, the count was right, but when I tried it on another virtual server (I changed the group ID and port) I get this:

PHP Code:

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Warning: preg_match(): Unknown modifier '9' in C:\xampp\htdocs\serverstatus\libraries\TeamSpeak3\Helper\String.php on line 192 


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That warning only shows up with some server groups, I don't know the reason.

---

PHP Code:

---

$admins = 0;
foreach($ts3->clientList($client) as $client) {
    $admins++;
} 


---

I guess this piece of code should show all online users but I tested it and the value is not always the online users, like I said before on my virtual server it shows the right count but when I tried it on another virtual server I got 48 but there are 61 users online.

TeamSpeak 3 PHP Framework