Can you please clear browser cache for npub.pro and try again? Choose notes, not posts.
Discussion
Yea I can do that
Getting this error message as well… 
Ah ok, I found this in logs, fixing, please wait a bit!
Fix deployed, you have 1-letter username which it tried to use as subdomain name for your site and failed, the error on the screenshot shouldn't happen now, please try again. Thank you!