It can be so hard to debug IndieWeb problems when they arise in Known. For now, this should be a webmention of the linked post, because Chris Aldrich reported a problem. But even if this works, I may need to go outside this installation to test properly. Or, perhaps, try webmention.rocks.
Sometimes, a man's gotta do what a man's gotta do. Like send a webmention to himself. Because someone else was getting an error when they tried to send one. And then, maybe, I can try using Telegraph to resend Chris' original.