Calibre Web Automated Kobo kepub download issue

Hi

I'm not sure anyone will be able to help as it's a bit of a niche question. I'm trying to use Calibre Web Automated without much success. Specifically when I try to convert a book to kepub I receive an error no 8 message - exec format error. I've downloaded the binary and put it in the usr/bin and set r w permissions so not sure what is going on.

Also does anyone know about book cover sizes? I've set a specific book cover size but when I download the book to my Kobo over the web it sets it to something else. I've run the cover enforcer command but this has made no difference.

Thank you