my First Admin Page is not shown up

I try to write a own module. After 1 week of searching I hope u can help to go on.

Its a very simple admin page.

module_dir: app/code/famberg/module_afterbuysync/

… Controller/Adminhtml/Settings/Index.php:

<?php
namespace FambergAfterbuySyncControllerAdminhtmlSettings;


use MagentoBackendAppActionAction;
use MagentoBackendAppActionContext;
use MagentoFrameworkAppActionHttpGetActionInterface;
use MagentoFrameworkViewResultPage;
use MagentoFrameworkViewResultPageFactory;

class Index extends Action implements HttpGetActionInterface
{
    const MENU_ID ="Famberg_AfterbuySync::settings";
    protected $_pageFactory;
    public function __construct(
                        Context $context,
                        PageFactory $pageFactory)
    {
        parent::__construct($context);  
        $this->_pageFactory = $pageFactory;
    }
    public function execute()
    {
        $resultPage = $this->_pageFactory->create();
        $resultPage->setActiveMenu(static::MENU_ID);
        $resultPage->getConfig()->getTitle()->prepend(__('AfterbuySync Settings'));
        return $resultPage;
    }
}
?>

…/etc/module.xml

<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:Module/etc/module.xsd">
    <module name="Famberg_AfterbuySync" setup_version="1.0.5">
    </module>
</config>

…/etc/adminhtml/routes.xml

<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:App/etc/routes.xsd">
    <router id="admin">
        <route id="afterbuysync" frontName="afterbuysync">
            <module name="Famberg_AfterbuySync" before="Magento_Backend" />
        </route>
    </router>
</config>

…/registration.php

<?php
use MagentoFrameworkComponentComponentRegistrar;
ComponentRegistrar::register(ComponentRegistrar::MODULE, 'Famberg_AfterbuySync', __DIR__);

Everytime i get the message

Invalid security or form key. Please refresh the page.

After xdebuging I see that the controller class is not loaded. The module is loaded. The menu item is shown. I dont know why the controller class does not exists.

Please help.
Michael