Php 无法从会话中设置电子邮件变量，因此mail（）函数无法工作

我对php和sql非常陌生，我正在尝试为我的用户电子邮件设置一个会话变量，我知道列名是正确的，我正在正确地从会话中提取其他信息，如用户id等，但似乎无法设置电子邮件，即使我与我的其他变量相同。我还尝试使用mail（）函数，但我不确定这是否设置正确？任何帮助都将不胜感激

我试着用一个隐藏的输入把这个变量作为一个_POST-one来处理，但也没有成功

    <div>

    <?php

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

    $user_email = $_SESSION['user_email'];
    $user_id = $_SESSION['user_id'];
    $first_name = $_SESSION['first_name'];
    $last_name = $_SESSION['last_name'];
    //  $request_time = date("d-m-Y H:i:s");
    $lend_status = 1;
    $requested_start_date = date('Y-m-d H:i:s', strtotime($_POST['requested_start_date'] . ' ' . $_POST['requested_start_time'] . ':00:00'));
    $requested_end_date = date('Y-m-d H:i:s', strtotime($_POST['requested_end_date'] . ' ' . $_POST['requested_end_time'] . ':00:00'));
    $comments = $_POST['comments'];


    // Declare available laptops array
    $available_laptops = array();

    // GET ALL LAPTOPS IN OPERATION
    $STH = $DBH->prepare("
        SELECT laptop_id,
        laptop_name
        FROM laptops
        WHERE 1
    ");
    $STH->execute(array());

    while ($row = $STH->fetch()) {

        // CHECK EACH LAPTOP FOR THE REQUESTED DATES
        $STH2 = $DBH->prepare("
            SELECT lend_id
            FROM laptop_system
            WHERE (
                (
                    approved_start_date <= ?
                    AND approved_end_date >= ?
                ) OR (
                    approved_start_date <= ?
                    AND approved_end_date >= ?
                ) OR (
                    approved_start_date >= ?
                    AND approved_end_date <= ?
                )
            )
            AND laptop_id = ?
        ");
        $STH2->execute(array(
            $requested_start_date,
            $requested_start_date,
            $requested_end_date,
            $requested_end_date,
            $requested_start_date,
            $requested_end_date,
            $row->laptop_id
        ));

        // IF IT'S NOT BOOKED OUT, ADD TO ARRAY
        if ($STH2->rowCount() < 1) {
            $available_laptops[$row->laptop_id] = $row->laptop_name;
        }
    }

    if (empty($available_laptops)) {

        echo '<h3>Sorry, this date is not available.</h3>';

    } else {

        $STH = $DBH->prepare("
            INSERT INTO laptop_system (
                user_id,
                first_name,
                last_name,
                lend_status,
                requested_start_date,
                requested_end_date,
                comments
            )
            VALUES(?, ?, ?, ?, ?, ?, ?)
        ");
        $STH->execute(array(
            $user_id,
            $first_name,
            $last_name,
            $lend_status,
            $requested_start_date,
            $requested_end_date,
            $comments
        ));

        echo '<h2 style="color:#D80B8C; margin-bottom:1em;">' . $first_name . ', your laptop request is now pending approval.</h2>';



        $to = $user_email;
        $subject = "Laptop Request";
        $message = "Thank you for your laptop request for " . $requested_start_date . " - " . $requested_end_date . "It is now pending and you will be notified if it's been approved or declined.";
        $message = wordwrap($message,70);
        $headers = "From: Timmy and Edwardo";

        mail($to,$subject,$txt,$headers);

    }

    } ?>


    <form action="" method="post" >

    <div>
      <label for="requested_start_date"> Requested Start Date </label>
      <input type="date" name="requested_start_date" value="<?php echo $requested_start_date; ?>">

        <label for="requested_start_time">Requested start time </label>
            <select name="requested_start_time" style="width:auto;margin:1em 1em 1em 0;">
                <?php   for ($i = 0; $i < 25; $i++) {$i = str_pad($i, 2, "0", STR_PAD_LEFT);  ?>
                    <option value="<?php echo $i; ?>"><?php echo $i . ':00'; ?></option>
                <?php } ?>
            </select>
    </div>

    <div>
      <label for="requested_end_date">Requested End Date </label>
      <input type="date" name="requested_end_date" value="<?php echo $requested_end_date; ?>">

        <label for="requested_end_time">Requested end time</label>
            <select name="requested_end_time" style="width:auto;margin:1em 1em 1em 0;">
                <?php   for ($i = 0; $i < 25; $i++) {$i = str_pad($i, 2, "0", STR_PAD_LEFT);  ?>
                            <option value="<?php echo $i; ?>"><?php echo $i . ':00'; ?></option>
                <?php } ?>
            </select>
        </div>

        <div>
            <p style="margin-bottom:0;">
                Please can you let us know below why you need the laptop and if there are any special requirements needed -
            </p>
          <input type="textarea" rows="4" cols="50" name="comments" placeholder="" required>
            <input type="submit" name="request_date" value="Request Date">
        <!--    <input type="hidden" name="user_email" value="<?php echo $user_email;?>" > -->
        </div>


    </form>


    <?php
    ?>
    </div>

执行
var\u转储（$\u会话）
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验证您试图读取的条目是否确实在其中。另外，如果您还没有启用正确的PHP错误报告，请启用它。