You have some options. But first make sure that your $ua accepts cookies and also has an acceptable user-agent string:

use HTTP::CookieJar::LWP ();
$ua = LWP::UserAgent->new;
my $jar = HTTP::CookieJar::LWP->new;
$ua->cookie_jar($jar);
$ua->agent('underage bot dont let me in!!!'); # <<< change that
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Bonus: using HTTP::Cookies::Mozilla can be helpful if you ever need to load firefox's cookie jar.