Nelze odeslat HTTP kód 500

<?php

class Trida {

    public function response404(string $reason = '') {

        //log reason
        if($reason !== '') {
            Debugger::log("HTTP 404 reason: $reason", LogLevel::INFO);
        }

        header("{$_SERVER['SERVER_PROTOCOL']} 404 Not Found", true, 404);
        echo 404;
    }

    public function response500(string $reason = '') {

        //log reason
        if($reason !== '') {
            Debugger::log("HTTP 500 reason: $reason", LogLevel::INFO);
        }

        header("{$_SERVER['SERVER_PROTOCOL']} Internal Server Error", true, 500); //problémová hlavička
        echo 500;
    }
}