it does not work

Sure it does. You've just forgotten to use the relevant modules. If we add those three important lines to the start of your code it does indeed run fine to completion.

use JSON;
use Encode;
use LWP::UserAgent;

# Original content follows, unedited
my @data = (); my $json_data = encode_utf8(encode_json(\@data));
my $ua = LWP::UserAgent->new;
my $request = HTTP::Request->new(POST => $url2);
$request->header("__atts" => $ajax_atts);
$request->header('__ath' => $ajax_ath);
$request->header('__atcrv' => $ajax_atcrv);
#$request->content($json_data);
my $response = $ua->request($request);
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