The download link looks good.
The downloaded file has the size it should.
But it isn't ientical to the source file and doesn't work.
$ ll sample.epub [= downloaded file]
-rw-r--r-- 1 gp gp 498797 19. Nov 23:29 sample.epub
$ ll tmp/sample.epub [= source file]
-rw-r--r-- 1 gp gp 498797 18. Nov 22:12 tmp/sample.epub
$ diff sample.epub tmp/sample.epub
Binary files sample.epub and tmp/sample.epub are different.
$ [files have same size and name but are different, download file does not work.]