Difficulties customising the marker tooltip

This page demonstrates how to customise tooltips however I am having difficulty in getting the Post ID to sent passed through so it can be used to add content to the tool tip.

For example, if I add this function, the post ID is not shown in the tool tip.

function my_wpgeo_point_title( $title, $post_id ) {
return $title . ‘ (Post ID=’ . $post_id . ‘)’;
}
add_filter( ‘wpgeo_point_title’, ‘my_wpgeo_point_title’ );

Any ideas what could be wrong?

https://www.ads-software.com/plugins/wp-geo/