Hi

That doesn't compile

Also, it is still incomplete

Still, if I go ahead and fill in the blanks by copying  dancer2 -a  HookTest I think I see what you see

You should read https://metacpan.org/pod/Dancer2::Plugin#Writing-the-plugin

This triggers

package TestHook;
use Dancer2::Plugin;

sub BUILD {
    my( $plugin ) = @_;
    $plugin->app->add_route(
        method => 'get',
        regexp => '/die',
        code   => sub { die "get '/die' => sub { " },
    );
    $plugin->app->add_route(
        method => 'get',
        regexp => '/ride',
        code   => sub { 'ride' },
    );
    $plugin->app->add_hook( Dancer2::Core::Hook->new(
        name => 'after_error',
#~         code => sub { $_[0]->content( $_[0]->content . " ... please
+?" ) }
        code => sub {
                   my $content = shift;
                   warn '      From TestHook From TestHook From TestHo
+ok From TestHook From TestHook      ';
                   $content->{content} .= " hello world From TestHook 
+ ";
                }
    ));
}

1;
__END__
[download]