Why is php not sending a UDP packet to the server?

Question

linux

There is a simple script

<?php
$server_ip   = $_POST['host'];
$server_port = $_POST['port'];

echo "Sending heartbeat to IP $server_ip, port $server_port\n";

if ($socket = socket_create(AF_INET, SOCK_DGRAM, SOL_UDP)) {
  for ($i = 1; $i <= 10; $i++) {
    $send_socket = socket_sendto($socket, $message, strlen($message), 0, $server_ip, $server_port);
    
    if($send_socket !== 0){
        echo "Сокет не отправлен.";
        var_dump($send_socket);
    }else{
        echo "Успеншо отправлен сокет";
    }

    sleep(1);
  }
} else {
  echo "Can't create socket";
}

The script works, I ran it on my computer, I send the UDP packet to the VPS, I check if the packets arrive in it with the command tcpdump -n udp port 4444
The same if done on a clean VPS, on which ubuntu20.04 and php7.4-fpm, the packets are sent to the server.

But if the script is run on some third-party server, UDP packets are not sent for some reason, socket_sendto returns bool(false), I also tested sending a UDP packet in C language, everything is the same for some reason, packets are not sent on third-party servers, what there may be a problem, please tell me.
I mean a third-party server, for example, hosting or just a VPS on which there is an admin panel for its administration.
Maybe the firewall prohibits sending packets or some rights are missing.

Answer 1

Check the firewall settings, both on the VPS and in the hosting panel, on the page where the network connection is configured (if any) - you need to make sure that traffic is allowed to pass through this port.