sitemap question

I have a dynamic website designed with Codeigniter 3 and I am working on the sitemap part as a newbie.
I found the library sitemap-php from evert/sitemap-php but I can't make it run.
From now this is what I did, I put the Sitemap.php file into my library folder
In my controller I enter the following

PHP Code:

public function Sitemap(){
$this->load->library('Sitemap'); 
$sitemap = new Sitemap('https://www.mywebsite.com');
$sitemap->setPath('/public_html/Sitemap/'); // I created a folder Sitemap into my public folder
$sitemap->setFilename('sitemap');
$sitemap->addItem('/', '1.0', 'daily', 'Today');
$sitemap->createSitemapIndex('https://www.mywebsite.com/sitemap/', 'Today');} 


Then when I go to https://www.mywebsite.com/sitemap/, I have an error 404.

Could you guide me to solve my issue.
Thanks