Monocle would not allow me to login using this site, saying there was no microsub endpoint. This was because in upgrading Known, I had forgotten that I had added the link to microsub before. I had also forgotten which of the hundreds of template files I had to edit in order to do that. In the end I found it with a brute-force search for all files ending in `.tpl.php` The file in question lives at `./IdnoPlugins/IndiePub/templates/default/indiepub/shell/head.tpl.php`.
Having found the correct file to edit, the rest was straightforward thanks to [excellent instructions.