I tried deploying my backend to Heroku and after I did that my website was still working on http://localhost:3000/ but after I build the app for deployment on GitHub Pages the website stopped working on the Github page but works on the local environment.
this is my GitHub repo: https://github.com/pranjalchaplot/missedmessage/
My deployed GitHub Page (doesn't work): https://pranjalchaplot.github.io/missedmessage/
Your JavaScript references are not set correctly as seen in your html javascript references, when you open that in a new tab, it feeds off of the "master" url, and brings you to a 404 page, you need to fix/change your reference path.
Also, the console is showing quite a few errors