I don't really understand your original macro but, at first glance, it looks like you are double-encoding -- the "sample output" in your last-but-one step contains "%250A"s, ie a URL encoded "%" symbol followed by "0A", rather then the "%0A"s I'd expect to be fed into the URL (though I don't know why that would result in the behaviour you're seeing!).
@Zirm, I think you're right -- Upnote simply doesn't accept line feeds (or carriage returns, or both together) in a callback URL. Other encoded characters do work -- although, since you can't use returns in search and replace, using eg "$$$$$" and replacing with line feeds later would be tricky.
You may need to go another route, like typing or pasting into a new note or saving out a text (or Markdown, if you've paid for Upnote) file and importing it.