Thank you for your answer.
How do I send specific values via API?
For example;
$url = 'https://101.101.101.101:8006/api2/json/nodes/<NODE>/qemu/';
$fields = array(
'vmid' => urlencode($_POST['vmid']),
'cores' => urlencode($_POST['cores']),
'sockets' => urlencode($_POST['sockets'])...