@Downes I don't know squat about WordPress ActivityPub plugins, but I'd wager the extra @ would be a problem. unless you get a better suggestion, and if it's not too difficult to make a new user just for testing, I'd try a username without an embedded @ ...other than that, I'd guess there's a log file on your http server that you can look at for PHP logs (I don't recall if WordPress also has it's own log file) that should give a hint @ton