Why forms are throwing a 400 error in heroku?

I made a project, Published it on Heroku

But unfortunately, none of the WTF-Forms are working, after they are submitted it throws a 400 error

When I run it locally, It works fine!

The Heroku site: https://library-managament-system.herokuapp.com/

Github Repo: https://github.com/LearnEarn-Fun/Library-Management-System

What is the problem? How can I make the forms to work??

Logs:

2021-07-01T07:13:31.976747+00:00 app[web.1]: 10.30.123.212 - - [01/Jul/2021:07:13:31 +0000] "POST /login HTTP/1.1" 400 7416 "https://library-managament-system.herokuapp.com/login" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/91.0.4472.124 Safari/537.36"
2021-07-01T07:13:32.482008+00:00 heroku[router]: at=info method=GET path="/static/css/styles.css" host=library-managament-system.herokuapp.com request_id=4c28d9f4-1fa1-4cd6-8921-44a95ad5add4 fwd="122.181.193.38" dyno=web.1 connect=1ms service=5ms status=304 bytes=178 protocol=https
2021-07-01T07:13:32.479098+00:00 app[web.1]: 10.30.123.212 - - [01/Jul/2021:07:13:32 +0000] "GET /static/css/styles.css HTTP/1.1" 304 0 "https://library-managament-system.herokuapp.com/login" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/91.0.4472.124 Safari/537.36"

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