Brave does not allow selecting *.epub files for upload from the browse file dialog. Only a few hours ago it was still possible.
Safari allows epub upload but instead of maintaining the epub format, the uploader extracts text from the epub and puts it in the “Paste Text” text area while horribly messing up the charset.
In case anyone else comes across this problem, I’ve copied and pasted part of my private email reply with the name of the epub changed to my-story.epub:
When I unzipped your attachment it behaved as you explained. I did a little investigating and it turns out that what looks like a file inside called my-story.epub is actually a directory. There’s an explanation as to why directories can look like files on macOS here: finder - What Makes an macOS "Package" Show as a Package? - Ask Different
I couldn’t find a simple way to fix Readlang so that it accepts uploading of these packages (directories that look like files) so what I did was to create a new .epub file for you by re-compressing the contents as a single file (a normal .epub file is also a .zip file):