Session variable appears empty on different page - php

Question

Edit: after doing some trial and error stuff I notice that if I comment the following code:
$success = $_SESSION["success"];
session_unset($_SESSION["success"]);
the $to variable displays as intended. So my question is why can't both be at the same time used?
Original question:
I'm trying to send an email using the mail() function. In order to do that I pass the variable $_SESSION['emailfrompass'] across 2 pages but for some reason the variable is always empty. Even though there is another variable that I send with a message and I have no problems in receiving it, this is the only one that makes problems
The session_start() is set across all pages. I tried using
ini_set('display_errors',1);
error_reporting(E_ALL);
for finding the problem but no use. The variable is always empty
This is my enterEFPass.php file. On top I have
<?php
session_start();
ini_set('display_errors',1);
error_reporting(E_ALL);
?>
<?php
if(isset($_SESSION["success"]))
{
$success = $_SESSION["success"];
session_unset($_SESSION["success"]); //echoing this will display the right thing
$to = "";
$to = isset($_SESSION['emailforpass']) ? $_SESSION['emailforpass'] : 'not found';
echo $to; //does not work
//mail($to, "Reset your password", $message, $headers);
?>
<div id='alert'>
<div class='alert alert-block alert-info'>
<?php
echo $success;
// echo "<script>setTimeout(\"location.href = 'login-page.php';\",2500);</script>";
?>
</div>
</div>
<?php
}?>
And this is the enterEFPass_route.php in which I instantiate the $_SESSION variables
<?php
session_start();
include 'db.php';
$email = "";
$conn = Connect();
if (isset($_POST['send_email_button']))
{
$email = mysqli_real_escape_string($conn, $_POST['email']); //$_POST['email'] the field where I introduce the email
}
if (empty($email)) { array_push($errors, "Please enter a valid email"); }
if (count($errors)==0) // just an array for error messages
{
$_SESSION['emailforpass'] = $email; //appears empty always
$_SESSION['success'] = "An email has been sent to the corresponding address. Please follow the instructions provided there"; //goes without problems
header("location: enterEFPass.php");
} else
{
$_SESSION['errormsgpassress']= $errors; //no problems in sending
header("location: enterEFPass.php");
}
}
?>
I expect the $to variable to print on the screen but it always prints "not found"
If I print $_SESSION['success'] there is no problems in that

Answer 1

The method session_unset() does not take any arguments. It is used to unset ALL session variables, thus it is unsetting the $_SESSION['success'] variable. See here for more details on that. Instead, use unset($_SESSION['success']); to unset a single session variable. Hope this helps!