if ( ! defined( 'ABSPATH' ) )
{
    exit;
}

function sillyplugin_display_settings_page()
{
    if ( ! current_user_can ( 'manage_options' ) ) return;
}
?>

<div class="wrap">
    <h1><?php echo esc_html( get_admin_page_title() ); ?></h1>
    <form action="options.php" method="POST">

    <?php
        settings_fields( 'sillyplugin_options' );
        do_settings_sections( 'sillyplugin' );
        submit_button();
    ?>

    </form>
</div>

<?php
function sillyplugin_add_toplevel_menu()
{
    // In order: page title, menu title, capability
    // slug, function, icon-url, position

    add_menu_page(
        'Silly Plugin Settings',
        'Silly Plugin',
        'manage_options',
        'sillyplugin',
        'sillyplugin_display_settings_page',
        'dashicons-admin-generic',
        null
    );

    add_action( 'admin_menu', 'sillyplugin_add_toplevel_menu' );
}

Uncaught Error: Call to undefined function get_admin_page_title() in /var/www/html/silly/wp-content/plugins/silly-plugin/silly-plugin.php:28
Stack trace:
#0 /var/www/html/silly/wp-settings.php(305): include_once()
#1 /var/www/html/silly/wp-config.php(94): require_once('/var/www/html/s...')
#2 /var/www/html/silly/wp-load.php(37): require_once('/var/www/html/s...')
#3 /var/www/html/silly/wp-admin/admin.php(31): require_once('/var/www/html/s...')
#4 /var/www/html/silly/wp-admin/plugins.php(10): require_once('/var/www/html/s...')
#5 {main}
  thrown in <b>/var/www/html/silly/wp-content/plugins/silly-plugin/silly-plugin.php</b> on line <b>28</b><br />