Peter’s Drupal site and my WordPress site don’t deal well with pingbacks. His doesn’t reliably send them, mine doesn’t listen as the endpoint (xmlrpc) is blocked by my hoster for security reasons. My site does process Webmentions. I came across Webmention.io, and it has an option to set my pingback ‘antenna’ to their server, which then transmogrifies and forwards it to my site’s webmention endpoint. This way pingbacks are dealt with on my end like webmentions, circumventing the trouble with my xmlrpc. I replaced the pingback url in my website’s section, by hand, which is not a sustainable option and likely only works until the next update of my WordPress theme. However the WordPress documentation is very silent on where in the database or back-end files I could change the pingback url as part of the bloginfo() settings function, and I can’t find it in the WordPress database or files.
I added a statement in the form of
<link rel="pingback" href="https://webmention.io/webmention?forward=https://www.zylstra.org/blog/wp-json/webmention/1.0/endpoint" />
to the file header file in the template from the back-end, not through the WP editor. It sets the pingback url to webmention.io with my own webmention endpoint as a forwarding address.