Fetch Request Form Data Shown As Null - php

Question

I new to PHP and this might not even be a problem. I have a JavaScript function that sends fetch request. When I send to the api.php, I get a null when I var_dump() the variable $studentnumber. I checked the fetch request and it's sending data in the request, so there is something wrong with PHP reading the form data... maybe?. Thanks in advance this was for a school assignment.
Fetch Request
function login() {
var studentnumber = document.getElementById("studentnumber");
var password = document.getElementById("password");
var logindetails = new FormData();
logindetails.append('studentnumber', studentnumber.value);
logindetails.append('password', password.value);
fetch('http://localhost/gaq/api/api.php?action=login', {
method: 'POST',
body: logindetails,
}
)
.then(function(response){
if (response.status == 202) {
var studentnumber = document.getElementById("studentnumber");
var logindetails = new FormData();
logindetails.append('studentnumber', studentnumber.value);
fetch('http://localhost/gaq/api/api.php?action=processlogin', {
method: 'POST',
body: logindetails,
});
console.log("Success");
} else {
console.log("Error");
}
})
}
API.PHP File
<?php
include 'database.php';
include 'session.php';
session_start();
//header('Content-Type: application/json');
$functions = new gaqfunctions();
if(!isset($_SESSION['user_session'])) {
$_SESSION['user_session'] = new gaqsession;
http_response_code(501);
die();
}
if(isset($_GET['action'])) {
switch($_GET['action']) {
case "login":
if($_SESSION['user_session']->userloginstatus()) {
$studentnumber = $_POST['studentnumber'];
$password = $_POST['password'];
$response = $_SESSION['user_session']->login($studentnumber, $password);
http_response_code(206);
if ($response == true) {
http_response_code(202);
} else {
http_response_code(404);
}
} else {
http_response_code(401);
}
break;
case "processlogin":
if($_SESSION['user_session']->userloginstatus()) {
$studentnumber = $_POST['studentnumber'];
var_dump($studentnumber);
//$studentnumber = isset($_POST['studentnumber']) ? $_POST['studentnumber'] : 0;
$_SESSION['user_session']->loginprocess($studentnumber);
http_response_code(206);
} else {
http_response_code(401);
}
break;
default:
http_response_code(400);
break;
}
}
?>