松弛通知无法通过php中的webhook工作

Question

I've create a little code in php to use in a slack webhook and I want to notify some user. I've put the @user in the string but in slack it doesn't notify them.

<?php

define('SLACK_WEBHOOK', '**********');

$array1 = array("@gfournier", "@cgagnon2", "@slaflamme", "@plgauthier");
$array2 = array();

for ($i = 0; $i < 4; $i++){
    $randInt = random_int(0, sizeof($array1)-1);
    array_push($array2, $array1[$randInt]);
    array_splice($array1, $randInt, 1);
}

$txt = "<@ithd> - :door: IT-Channel:slack: Random text: :slack:IT-Channel :door: 
 Lundi à Mercredi: " . $array2[0] . " - " . $array2[1] . "
 Jeudi et vendredi: " . $array2[2] . " - " . $array2[3];

echo $txt;

$message = array('payload' => json_encode(array('text' => $txt)));


$c = curl_init(SLACK_WEBHOOK);
curl_setopt($c, CURLOPT_SSL_VERIFYPEER, false);
curl_setopt($c, CURLOPT_POST, true);
curl_setopt($c, CURLOPT_POSTFIELDS, $message);
curl_exec($c);
curl_close($c);
?>

I want the notification to work in slack.

Thanks