javascript - Set and get session variables in PHP through fetch API

one text

I am trying to set a session variable using fetch -

const response = await fetch('http://locahost/index.php/session/set', {
      method: 'POST',
      credentials: 'include',
      headers: {
        'Content-Type': 'application/json'
      },
      body: JSON.stringify({token:"token"})
});

The PHP function (inside a class) that does this -

public function setSession($arr){
try{
     session_start();
     $_SESSION['token'] = $arr['token'];
     $responseData = json_encode("SESSION token has been set to ".$_SESSION['token']);
     /// sendresponsedata() -> send response back with Access-Control-Allow-Credentials: true
    } catch (Error $e) {
       /// Some error
    }
} 

The PHP function is not on the same page as the page making the fetch request. When I console.log the response on the page that sent the request, it correctly shows SESSION token has been set to token.

But if then I try to retrieve the session variable using a different request and a different function -

fetch('http://localhost/index.php/session/get',{
    credentials: 'include'
  })

The response I get from this is always No ongoing session

public function getSession(){
try {
      session_start();
      // print json_encode($_SESSION); <---- printing this shows an empty array
      $responseData = json_encode((isset($_SESSION["token"])) ? $_SESSION["token"]:"No ongoing session");
      /// sendresponsedata() -> send response back with Access-Control-Allow-Credentials: true
     } catch (Error $e) {
      /// Some error               
     }
}

I looked at other questions like mine but as far as I could understand, the error was because of not allowing credentials. I couldn't really understand why credentials are needed in this case reading this, but I added them anyway to check first, but that didn't change anything. As far as I could understand fetch request creates a new session everytime so this could be impossible, but this might be possible if I made an AJAX request. I am not sure I understood that correctly however.

The sendresponsedata() function works well as I have made many other fetch requests with more headers, like allowing cross-origin requests and returning required headers on preflight handshakes which all worked (and it is not really a complicated function).

What am I doing wrong and how can I achieve what I need?

Edit: Since posting I have also tried xhr requests and they don't work either.