You need to make sure you have:
use Links::Plugins;
....at the top to be able to use get_plugin_user_cfg
Or change:
my $sdv = Links::Plugins->get_plugin_user_cfg('SecondDetailed');
to
require Links::Plugins;
my $sdv = Links::Plugins->get_plugin_user_cfg('SecondDetailed');
use Links::Plugins;
....at the top to be able to use get_plugin_user_cfg
Or change:
my $sdv = Links::Plugins->get_plugin_user_cfg('SecondDetailed');
to
require Links::Plugins;
my $sdv = Links::Plugins->get_plugin_user_cfg('SecondDetailed');