php server request method is not changing

Question

im following a video to creat JSON CRUD project, after watching the tuto i download the project file, started a server and put the files in it, but it was not working as i expect, after while i found out the problem could be the server quest method, in the vid, teacher click the submit button the method change to POST, but in my script it still apearing GET, how can i fix it ,

<?php
include 'partials/header.php';
function getUsers()
{
    return json_decode(file_get_contents(__DIR__ . '/users/part.json'), true);
}

function getUserById($id)
{
    $users = getUsers();
    foreach ($users as $user) {
        if ($user['id'] == $id) {
            return $user;
        }
    }
    return null;
}

function createUser($data)
{
    $users = getUsers();

    $data['id'] = rand(1000000, 2000000);

    $users[] = $data;

    putJson($users);

    return $data;
}

function updateUser($data, $id)
{
    $updateUser = [];
    $users = getUsers();
    foreach ($users as $i => $user) {
        if ($user['id'] == $id) {
            $users[$i] = $updateUser = array_merge($user, $data);
        }
    }

    putJson($users);

    return $updateUser;
}


$userId = 2;

$user = getUserById($userId);
if (!$user) {
    include "partials/not_found.php";
    exit;
}

$errors = [
    'time' => "",
    'part' => "",

];

if ($_SERVER['REQUEST_METHOD'] === 'POST') {
    $user = array_merge($user, $_POST);

    $isValid = validateUser($user, $errors);

    if ($isValid) {
        $user = updateUser($_POST, $userId);
        uploadImage($_FILES['picture'], $user);
        header("Location: index.php");
    }
}

?>

<div class="container">
    <div class="card">
        <div class="card-header">
            <h3>
                <?php if ($user['id']): ?>
                    Update user <b><?php echo $user['id'] ?></b>
                <?php else: ?>
                    Create new User
                <?php endif ?>
            </h3>
        </div>
        <div class="card-body">

            <form method="POST" enctype="multipart/form-data"
                  action="">
                <div class="form-group">
                    <label>Time</label>
                    <input name="name" value="<?php echo $user['time'] ?>"
                           class="form-control <?php echo $errors['time'] ? 'is-invalid' : '' ?>">
                    <div class="invalid-feedback">
                        <?php echo  $errors['time'] ?>
                    </div>
                </div>
                <div class="form-group">
                    <label>part</label>
                    <input name="username" value="<?php echo $user['part'] ?>"
                           class="form-control <?php echo $errors['part'] ? 'is-invalid' : '' ?>">
                    <div class="invalid-feedback">
                        <?php echo  $errors['part'] ?>
                    </div>
                </div>
              

                <button class="btn btn-success">Submit</button>
            </form>
        </div>
    </div>
</div>

the original youtube link the submit part is at 26:00 ish

and my online version is here