I have tried to duplicate an app, and create a new one, but no matter what I get this error.
Hi @WillM 
Just to double-check, do you still have the error if you refresh the page and enter a more unique name for the app?
@WillM Hmm, it sounds like there’s a Bubble bug; you can report this here:
In the meantime, there was another post which said closing the browser completely, and then trying again at least temporarily solved the issue. That might be worth a try for now
Done.