$_SESSION variable not saving between pages PHP [duplicate] - php

Question

This question already has answers here:
Session variables not working php
(12 answers)
Closed 4 years ago.
Im trying to save my username to the SESSION variable using a login system however it doesn't save.
I tried printing the session variable straight away in the same page and that works however when i go to another page, it won't save.
I'm very new this stuff so im sorry if it's something obvious :)
Any help will be much appreciated :)
PHP CODE 1:
$app->post('/api/customer/login/{Username}/{PassW}', function(Request $request, Response $response){
$Username = $request->getParam('Username');
$PassW = $request->getParam('PassW');
$PassW = md5($PassW);//FIND NEW WAY OF HASHING AS MD5 IS DEPRECIATED
$sql = "SELECT * FROM login WHERE Username= '$Username' AND PassW='$PassW' LIMIT 1";
try{
$db = new db();
$db = $db->connect();
$stmt = $db->query($sql);
$result = $stmt->fetchAll(PDO::FETCH_ASSOC);
if(count($result) == 1){
session_start();
$_SESSION['Username'] = $Username;
echo "<script type='text/javascript'>alert('Correct!');
window.location='http://localhost/testing/dashboard.php';
</script>";
exit();
PHP CODE 2 (The next page):
This page is simply a HTML page with other stuff but has the below PHP code in its body to test if its saved the variable.
<?php
session_start();
print_r($_SESSION);
?>

Answer 1

This code is missing the session_start(): PHP CODE 2 (The next page)
It should have been:
<?php
session_start();
print_r($_SESSION);
?>

Answer 2

whenever you use session on the page so you must start the session on that page so your code on code 2 page should be like this
<?php
session_start();
print_r($_SESSION);
?>
also, add the same line on a login page
session_start();
if everything seems fine to you then try to remove the cache from your browser as you are using javascript to redirect the page and there might be a chance that browser is loading the page from cache.