unable to get session username to insert to database [closed]

Unable to insert session id to database. I Want to get the session username and insert it to database and display the current session username content.

<?php
require("session.php");
require ("include.php");

if (isset($_POST['save'])) {

    if (
        !empty($_POST['name']) && !empty($_POST['subject']) && !empty($_POST['sender']) &&
        !empty($_POST['to'])) 
    {
        $session_id = $_SESSION["user"];  
        $name = $_POST['name'];
        $subject = $_POST['subject'];
        $sender = $_POST['sender'];
        $to = $_POST['to'];
        $time = date("Y-m-d H:i:sa");

        foreach ($name as $key => $names) {
            $s_name = $names;
            $s_subject =  $subject[$key];
            $s_sender = $sender[$key];
            $s_to = $to[$key];
            $save = mysqli_query($link,"INSERT INTO `incomings`( `name`, `subject`,`sender`, `to_`,
`session_id`,  `time`) VALUES ('$s_name','$s_subject','$s_sender',  
'$s_to','$session_id', '$time' )");
            $save_q = mysqli_query($link,$save);
        } 

        if (!$save) {
            echo " Mails Not Submitted!";
            header("Location:insert_incoming.php");
            exit(0);} 
    }
}
?>