it uses Geany's own `utils_open_browser()`, so that suggests this doesn't work for you either?
I had seen the browser setting, but don't know what actually uses it. Same with the terminal command. What actually uses it? I also often have ... "send selection to" not working until I restart geany. I'm close to being annoyed enough with it to search for the problem.
Though, note that the default behavior is to show the URL, not open it.
It didn't appear to do either. No popup or message in status or msgwin on success. I don't recall seeing anything but some usual gtk errors in terminal.
... by default the pastes are deleted after a while, and it just means that nobody had made a forever-paste since then.
I don't see how to use the geany pastebin service without the plugin. There's no web form I can find.