send a JSON data object to the server using Javascript XMLHttpRequest?

Question

Im conding in php and would like to send the information on the calender to the controller. I think my MVC is set up correctly and i get a status 200 that the data is sent as an object (see photo) but when i want to receive it in the controller i keep getting NULL. My project does not have a .htacess and uses a basic router. I run everthing form my docker container. The idea is click a tile and sent the object information to the controller so i can add it to a shoppingcart. Any help is appreciated

this is the code that i was trying in my javascript

document.addEventListener('DOMContentLoaded', function() {
document.querySelectorAll('.event').forEach(function(eventElement) {
    eventElement.addEventListener('click', function() {
        var eventDetails = {
            name: this.getAttribute('data-name'),
            startTime: this.getAttribute('data-start-time'),
            endTime: this.getAttribute('data-end-time')
        };
        // Send AJAX request to the server
        var xhr = new XMLHttpRequest();
        xhr.open('POST', 'http://localhost/jazz');
        xhr.setRequestHeader('Content-Type', 'application/json');
        xhr.onreadystatechange = function() {
            if (xhr.readyState === XMLHttpRequest.DONE) {
                if (xhr.status === 200) {
                    console.log(eventDetails);
                    console.log('Request successful');
                } else {
                    console.error('Request failed');
                }
            }
        };
        xhr.send(JSON.stringify(eventDetails));
    });
  });
});

This is my controller where i want to receive the information but the vardump is empty and it does not go in the if-statement

OUTPUT - var_dump($requestData) = string(0) ""
OUTPUT - var_dump($_SERVER['REQUEST_METHOD']) = string(3) "GET"
OUTPUT - var_dump($selectedEventData) = NULL
OUTPUT - var_dump($_REQUEST) = array(4) { ["PHPSESSID"]=> string(32) 
"5c37a82703acc9f86f54c3817f08c4e9" ["pma_lang"]=> string(2) "nl" 
["phpMyAdmin"]=> string(32) "18b3f28efd9ffb94e2c3a28ae292819f" 
["pmaUser-1"]=> string(60)  
"JNBvWJn0SxdqeVHqQN1vIu7Hx4P9BdLusicXILkrWFCTKGhrT1VLLIUcFxw=" }

jazzcontroller.php:

    $requestData =  file_get_contents("php://input");
    var_dump($requestData);
 
    var_dump($_REQUEST);
    $selectedEventData = json_decode($requestData, true);
    var_dump($selectedEventData);
    if ($selectedEventData) {
        var_dump($selectedEventData);
        $selectedEventDetails = new EventMusic();
        $selectedEventDetails->getArtist()->setName($selectedEventData['name']);
        $selectedEventDetails->setStartTime($selectedEventData['startTime']);
        $selectedEventDetails->setEndTime($selectedEventData['endTime']);

this is my router <?php

namespace Routers;
use Exception;

class PatternRouter {

private function stripParameters($uri)
{
    if (str_contains($uri, '?')) {

        $uri = substr($uri, 0, strpos($uri, '?'));
    }
    return $uri;
}

public function route($uri)
{
    // Check if there's an api request
    $api = false;
    if (str_starts_with($uri, "api/")) {
        $uri = substr($uri, 4);
        $api = true;
    }

    //Check if there's an request to the CMS
    $cms = false;
    if (str_starts_with($uri, "cms/")) {
        $uri = substr($uri, 4);
        $cms = true;
    }

    // Set default controller & method
    $defaultcontroller = 'home';
    $defaultmethod = 'index';

    // Ignore query parameters
    $uri = $this->stripParameters($uri);

    // Read controller & method names from URI
    $explodedUri = explode('/', $uri);

    if (!isset($explodedUri[0]) || empty($explodedUri[0])) {
        $explodedUri[0] = $defaultcontroller;
    }
    $controllerName = $explodedUri[0] . "controller";

    if (!isset($explodedUri[1]) || empty($explodedUri[1])) {
        $explodedUri[1] = $defaultmethod;
    }
    $methodName = $explodedUri[1];

    // Require the file with the controller class
    $className = "Controllers\\" . $controllerName;

    if ($api) {
        $className = "ApiControllers\\" . $controllerName;
    }

    // Dynamically call controller & method
    try {
        $controllerObj = new $className;
        $controllerObj->{$methodName}();
    } catch (Exception $e) {
        http_response_code(404);
        // die();
    }
  }
}

Thanks again for all the feedback, I kept trying with no result e.g. changing the javascript code to send the data differently (without sending object) but no luck yet. I will keep trying