Apparently something about Postmarks makes Share Openly think it’s a Mastodon instance, (to be fair, it is an ActivityPub server), so SO is trying to post to /share with a single text entry instead of /bookmarks/new with the url as defined in the link element.
Wondering if it’s better to (a) write an Nginx redirect, (b) write a redirec in Postmarks and submit a patch for it, or (c), report the issue to ShareOpenly.
Whatever I end up doing, it’ll have to be later.