Multipage Dashboard Callback Error

I am trying to build a multipage dash board.
I can’t add any particular code.
In this GitHub repo I have a folder of data and a folder (app) of pages.
Dashboard Code

I am following this documentation ( URL Routing and Multiple Apps | Dash for Python Documentation | Plotly). But somehow the callback function is not working.

The function related to each callback is not working properly. That’s why the data/chart is not getting loaded.

I have found a solution.
I have kept this line in each page:

app = dash.Dash(__name__)

That’s why the callback was not working.