Deployment 404 not found error

Hi,
I just started using Github, and I realized that my code was rather properly written and I was able to publish it as well, but for some very odd reason “Page not found” error kept popping up. Even after downloading the Deploy, as instructed, I can see that the downloaded “published” file has the “index.html” in it. Would you be able to assist me with this?

The relevant site name is…?