WordPress pages (as opposed to posts) do not have pingback and trackback support by default. I had a need to enable it on The New Leaf Journal in order to allow certain pages to accept incoming Webmentions. In that case, I added the PHP snippet to my child theme’s functions.php file. But with multiple sites and the possibility that I may not always use the same theme, I decided to convert the snippet into a site-specific plugin. The code is available in my personal Gitea repository. Feel free to use and extend (instructions for extending are in the code comments).