@pfefferle I had a hunch that it was being caused by the plugin trying to send webmentions from a url with the www prefix. Once I changed my site url in my settings to not include it, they started sending again.
Looks like the WordPress Webmention Plugin hasn’t been working for me for some time now. I’ve been trying for a while to troubleshoot it but I’m coming up running out of ideas. Seems like I can send them fine manually, they won’t send when posts are published.
The idea of posting on your blog and cross-posting to lots of place is the right idea, no argument there, the problem is that the places you can actually cross-post to are few and far-between. The two places mentioned in the article that can peer with most other blogging software are micro.blog and WordPress. Everything else as far as I know, if you want to peer with them in a POSSE-like way, requires you to remove features from your writing, and you have to decide if it’s worth it.