Change page after login

i'm trying to develop an interface for a db but I am not very practical in php. What I would like to do is showing the homepage after loggin in. However, the redirection does not work.

Desired behavior: 1) index.php -> login form / login credential

2) the credential login is sent to authenticate.php and if everything is correct, the homepage is viewed

Current behavior: Once the credentials are sent, authenticate.php does not change the page in homepage.php but remains a blank page.

authenticate.php

<?php require_once ('connect.php');
ob_start();
session_start();

// Now we check if the data was submitted, isset will check if the data exists.
if ( !isset($_POST['username'], $_POST['password']) ) {
    // Could not get the data that should have been sent.
    die ('Username and/or password does not exist!');
}

if ($stmt = $connect->prepare('SELECT username, password FROM user WHERE username = ?')) {
    // Bind parameters (s = string, i = int, b = blob, etc), hash the password using the PHP password_hash function
    $stmt->bind_param('s', $_POST['username']);
    $stmt->execute();
    $stmt->store_result();

    // Store the result so we can check if the account exists in the database.
    if ($stmt->num_rows > 0) {
        $stmt->bind_result($username, $password);
        $stmt->fetch();
        $hash = hash('sha256', $_POST['password']);

        // Account exists, now we verify the password.
        if (hash_equals($password, $hash)) {
            $_SESSION['loggedin'] = TRUE;
            $_SESSION['username'] = $_POST['username'];

            header('Location: homepage.php');
            $output = ob_get_clean();
        } else {
            echo 'Incorrect username and/or password!';
        }

    } else {
        echo 'Incorrect username and/or password!';
    }
    $stmt->close();

} else {
    echo 'Could not prepare statement!';
}
?>

connect.php

<?php
$config = parse_ini_file('pathToFile...\credential.ini');
$connect = @mysqli_connect('localhost',$config['username'],$config['password'],$config['dbname']);
unset($config);
?>