Why is the IP address of each of my registered users displayed as 0.0.0.0? I can be sure that the code is correct

if(trim( $_POST['password'])!=trim($_POST['firmPassword'])){

exit("The passwords entered twice are inconsistent");

}

$userName=trim($_POST['userName']);

$password=md5(trim($_POST['password']));

$time=time ();

$ip=ip2long($_SERVER['REMOTE_ADDR']);

echo $ip;

$conn=mysqli_connect("localhost","root ","");

if(mysqli_errno($conn)){

echo mysqli_error($conn);

exit;

}

mysqli_set_charset($conn, 'utf8');

mysqli_select_db($conn,'zhuce_php');

$sql = "insert into user(`userName`,` password`,`createtime`,`createip`) values ('"

. $userName . "','" . $password . "','" . $ time . "','" . $ip . "')";

$result=mysqli_query($conn,$sql);

echo 'The ID inserted by the current user is:' .$conn->insert_id;

if($result){

echo "Success
";

}else{

echo "Failed";

}

mysqli_close($conn);

?>