How to call d.multicall2

I'm trying to call an API using PHP xml-rpc. Here is the API I'm trying to retreive : https://rtorrent-docs.readthedocs.io/en/latest/cmd-ref.html#term-d-multicall2

So far I made the following :

<?php
$username "test";
$password = "test";
function do_call($username, $password, $request) {

    $url = "https://$username:$password@example.com:32491/RPC2";
    $header[] = "Content-type: text/xml";
    $header[] = "Content-length: ".strlen($request);

    $ch = curl_init();
    curl_setopt($ch, CURLOPT_URL, $url);
    curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
    curl_setopt($ch, CURLOPT_TIMEOUT, 1);
    curl_setopt($ch, CURLOPT_HTTPHEADER, $header);
    curl_setopt($ch, CURLOPT_POSTFIELDS, $request);

    $data = curl_exec($ch);
    if (curl_errno($ch)) {
        print curl_error($ch);
    } else {
        curl_close($ch);
        return $data;
    }
}
//$request = xmlrpc_encode_request("download_list", array()); //Give torrents hash
$request = xmlrpc_encode_request("d.multicall2", array("main", "d.name="));

$response = do_call($username, $password, $request);
var_dump($response);

Result :

string(310) " faultCode -501 faultString Unsupported target type found. "

Example call with xmlrpc :

rtxmlrpc --repr d.multicall2 '' tagged d.hash= d.name= d.custom=category

I don't understand why I'm getting this error

rTorrent version : 0.9.7/0.13.7

In issue 227 rakshasa says:

All commands are supposed to include a target as the first parameter, in this case an empty string.

So you need to call like this see the first empty string: $request = xmlrpc_encode_request("d.multicall2", array("", "main", "d.name="));