Unable to open the Epub file

[SundeepPidugu]

I was able to run the file and generate the Epub file but i was not able to open the file on any of the ebook readers(tried with Microsoft edge and calibre).
Error message:

calibre, version 3.42.0
ERROR: Could not open e-book: Failed to read book, /home/liferay172/Documents/Sundeep/book.epub click "Show Details" for more information

Traceback (most recent call last):
  File "site-packages/calibre/utils/ipc/simple_worker.py", line 291, in main
  File "site-packages/calibre/ebooks/oeb/iterator/book.py", line 65, in extract_book
  File "site-packages/calibre/customize/conversion.py", line 245, in __call__
  File "site-packages/calibre/ebooks/conversion/plugins/epub_input.py", line 268, in convert
  File "site-packages/calibre/utils/localunzip.py", line 233, in extractall
  File "site-packages/calibre/utils/localunzip.py", line 220, in _extractall
ValueError: Not a ZIP file

How do i fix this.