I have been looking for a way to syndicate from here to Mastodon, and landed on the KnownMastodon plugin. Unfortunately, that did not work for me. I did a bit of digging and discovered that the error was in a piece of Mastodon authorisation code and that cdn has implemented a fix, but that did not seem to have made it into the code I downloaded. Further digging revealed that the fix was actually by crscheid and that even though they had created a proper pull request, that had not been merged either. I did what any sane cargo culter would do, downloaded the fix, stuck it in my site, crossed my fingers and tried again. Lo!