This works for me:

my $vm_view = Vim::find_entity_views(
    view_type => 'VirtualMachine',
    filter    => { 'name' => name of your vm' },
    properties => ['summary.customValue', ],
);


for my $value ( @$vm_view ) {
    my $cv_ref = $value->{'summary.customValue'};
    for ( @$cv_ref ) {
        print "key: ", $_->key, "\tvalue: " , $_->value, "\n";
    }
}