@zserge Thanks for being part of the GitHub Community Forum and for asking about this.

As the error message indicates, going through the options in the Help article can help. Because you specifically mentioned that your site is static HTML/CSS with no Jekyll, the easiest fix would be to disable Jekyll by adding a .nojekyll file like described here.

If that still doesn’t do the trick, then I’d recommend reaching out to us via private support at https://github.com/contact so that we can look a little closer at your account details to see what the problem may be.

Thanks again, @zserge! Let me know if you have further questions.

Cheers!