The primary purpose of your app is to paste some JSON then send someone a URL to access it, right?
If a user pastes some JSON, clicks the Access URL text box, presses Command-A Command-C to copy the URL, then pastes it to someone else, that person won't be able to open the URL, because it lacks a "https: prefix. That's probably a bug, whether or not it's an intended feature.
It's not something that matters very much, but your users might be slightly annoyed at having to chop off the leading "//" every time they want to copy the URL.
I admit I might be missing something obvious, though.