Though I have not worked directly with Paypal, here is a chunk of code I use in working with one of the bigger gateways, FWIW:

use HTTP::Request::Common;
use LWP::UserAgent;
my $ua = LWP::UserAgent->new;
my $req = POST 'http://www.somegateway.com/cgi-bin/somedir',
[    
    somevariable1         => 'foo',
    somevariable2         => 'bar',
];

my $reply;
my $response = $ua->request($req);
    if ($response->is_success) {
        $reply = $response->content;
    } else {    
      print STDERR $response->status_line, "\n";
    }

...do something with $reply...
[download]

Usually there are parameters that I send (like credit card info) and then I get a reponse code that I parse (such as 'approved', 'declined').