Error was:
Docverter::APIError: Docverter API Error: command error: ebook-convert: error while loading shared libraries: libcalibre-launcher.so: cannot open shared object file: No such file or directory
was able to resolve by heroku config:add LD_LIBRARY_PATH=/app/calibre/lib
Heroku is not detecting calibre library path.
Error was: Docverter::APIError: Docverter API Error: command error: ebook-convert: error while loading shared libraries: libcalibre-launcher.so: cannot open shared object file: No such file or directory
was able to resolve by
heroku config:add LD_LIBRARY_PATH=/app/calibre/lib