Adding updates/notes/comments to an issue/request

I'm trying to work out how to get a Fusion workflow to add an update/note/comment to a request (issue) but I seem to be missing the obvious as I can't work it out. All I want to do is post "this action was performed by Fusion automation" so it's clear that it wasn't done manually.

I've seen suggestions that this could be done through either an "create record" module or a custom API post but I've not had any success in doing this. Which field should I be using and which module is best suited for this?