Notice (1024): Undefined property: ErrorController::$Authentication in /var/www/petz-rechnung/src/Controller/AppController.php on line 77 [CORE/src/Controller/Controller.php, line 314]
Warning (512): Unable to emit headers. Headers sent in file=/var/www/petz-rechnung/vendor/cakephp/cakephp/src/Error/Debugger.php line=831 [CORE/src/Http/ResponseEmitter.php, line 72]
Warning (2): Cannot modify header information - headers already sent by (output started at /var/www/petz-rechnung/vendor/cakephp/cakephp/src/Error/Debugger.php:831) [CORE/src/Http/ResponseEmitter.php, line 169]
Warning (2): Cannot modify header information - headers already sent by (output started at /var/www/petz-rechnung/vendor/cakephp/cakephp/src/Error/Debugger.php:831) [CORE/src/Http/ResponseEmitter.php, line 198]
Error: Controller class Sitemap.xml could not be found.

Controller class Sitemap.xml could not be found.

Cake\Http\Exception\MissingControllerException
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/var/www/petz-rechnung/vendor/cakephp/cakephp/src/Controller/ControllerFactory.php Toggle Arguments
     * @return void
     */
    protected function missingController(ServerRequest $request): void
    {
        throw new MissingControllerException([
            'class' => $request->getParam('controller'),
            'plugin' => $request->getParam('plugin'),
            'prefix' => $request->getParam('prefix'),
            '_ext' => $request->getParam('_ext'),

If you want to customize this error message, create templates/Error/error500.php