function setFooter($text, string $iconurl = '') {
        $text = (string) $text;
        
        if(\mb_strlen($text) > 2048) {
            throw new \InvalidArgumentException('Footer text can not be longer than 2048 characters.');
        }
        
        $this->footer = array(
            'text' => $text,
            'icon_url' => $iconurl
        );
        
        return $this;
    }