I have been working on a different Obsidian plugin for no good reason than to do it and I spent much more time than I would like to admit doing so. However, after a lot of trial and error I was able to figure out how to update posts using post_id vs just normal url. At some point I need to write this out in more detail but this is all for now.
If all goes well this should post from this plugin as well.
It did POST and now the update works successfully too! 🥳