Solved the issue by actually receiving the body as json format in my php and sending it back in the same format

$jsonData = file_get_contents('php://input');
    $data = json_decode($jsonData, true);
    if ($data !== null) {
    $name = $data['username'];
        echo json_encode($name);
    } 
    else {
        echo json_encode('e no work');
    }