friendica-addons/advancedcontentfilter/src/middlewares.php

<?php

$container = $slim->getContainer();

// Error handler based off https://stackoverflow.com/a/48135009/757392
$container['errorHandler'] = function () {
	return function(Psr\Http\Message\RequestInterface $request, Psr\Http\Message\ResponseInterface $response, Exception $exception)
    {
        $responseCode = 500;

		if (is_a($exception, 'Friendica\Network\HTTPException')) {
			$responseCode = $exception->httpcode;
		}

		$errors['message'] = $exception->getMessage();

        $errors['responseCode'] = $responseCode;

        return $response
            ->withStatus($responseCode)
            ->withJson($errors);
    };
};

$container['notFoundHandler'] = function () {
    return function ()
	{
		throw new \Friendica\Network\HTTPException\NotFoundException(L10n::t('Method not found'));
    };
};