@john @mastohost 422 usually means there’s a problem with the message body. Check the recipe and make sure it includes the status= part. That seems to be the most common problem.
Are you using more than one parameter in the message body? (Visibility or spoiler_text, for instance) I’ve only done a little experimenting with that, so I don’t know if the order makes any difference. Or maybe there’s an & in the text and Mastodon is treating it as a separator?
I should really test how flexible it is