Kat's advice is sound. Here's my takeaway:
1) Have the protagonist solve the final problem.
2) Make sure the protag has earned any victory through growth, courage, self-sacrifice, and hard work.
3) Ensure all tools the protag and antag use have been woven and layered in throughout the book.
4) Take time for wrap-up in the denouement, hinting at how the protag's growth will change the world around her going forward.
Read the full article:
And for further information on climaxes and endings:
Write a satisfying climax,