What am I doing wrong?

Except for posting a password on a public website? ;) You aren't using strict and warnings. You are using C style for loop (not really wrong, but not very perlish). You're adding "\n\n" to the result returned by the credentials method, which is useless. And the first argument of the credentials is wrong. Here's a working example:

use 5.010;
use strict;
use warnings;
use LWP::UserAgent;

my @sites = (
    "searchjid.usa.np.community.playstation.net",
    "searchjid.eu.np.community.playstation.net",
    "searchjid.jpn.np.community.playstation.net",
);
my $path = "/basic_view/func/search_jid";
my $user = "c7y-basic01";
my $pass = "A9QTbosh0W0D^{7467l-n_>2Y%JG^v>o";

for (@sites) {
    my $browser = LWP::UserAgent->new;
    $browser->agent("PS3Community-agent/1.0.0 libhttp/1.0.0");
    $browser->credentials( "$_:80", "c7y-basic", $user => $pass );
    say $browser->head( "http://" . $_ . $path )->as_string;

}
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