[DEV HELP] APIHandler - how to use it in the generic plugin


I want to use the APIHandler class in my generic plugin but I can’t figure out the way how to use it.
I know how to use a normal Handler class - using LoadHandler hook - and everything would be fine making it that way but I really need to have control over HTTP status codes, proper JSON response, etc and for that I need APIHandler.

Is there someone who made it? Or someone who can help me or tell me if it is even possible?

What I did already:
I registered to the Hook named LoadHandler, like that:

 if ($this->getEnabled() && $page == 'pluginapisite') {
        define('HANDLER_CLASS', 'PluginApiHandler');
        return true;

In PluginApiHandler:

  function getEndpointPattern: 
  	return $this->_pathPattern = '/{contextPath}/' . $this->_handlerPath;


 $this->_handlerPath = 'pluginapisite';
 $this->_endpoints = array (
    'GET' => array (
             array (
                    'pattern' => $this->getEndpointPattern(), 
                    'handler' => array($this, 'getSmthng')

And the biggest problem for me right now is to not get 404, at: https://website.com/index.php/Journal/pluginapisite

What should I do with index function?

Is this even possible to make it this way?