The SYNOPSIS from the POD of Net::Appliance::Session shows how to get more information when it "does not seem to be working":

try {
    $s->connect({ username => 'username', password => 'loginpass' });
 
    $s->begin_privileged({ password => 'privilegedpass' });
    print $s->cmd('show access-list');
    $s->end_privileged;
}
catch {
    warn "failed to execute command: $_";
}
finally {
    $s->close;
};
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See also the Basic debugging checklist