I am trying to deploy a simple flask app with ReactJS as Frontend on Azure Web Service. Below is my dir structure:

In locally, I can run this app by firing the below commands:
flask run <--Backend
npm start <--- Front end
In my server.py, I have ensured that this app can be accessed from outside:
if __name__ == "__main__":
app.run(host='0.0.0.0',debug = True)
All things are running locally fine as expected. Then I deployed this to Azure App Service using Azure DevOps. I have also ensured the startup script as per Microsoft Documentation:
gunicorn --bind=0.0.0.0 --timeout 600 --chdir flask-server server:flaskreactapp
Unfortunately, when I am browsing the url "https://mysampleapp.azurewebsites.net", nothing is showing up. Instead it is giving Application Error
Not able to understand what I am missing here.
Just a thought here, in order to run this locally, I am firing two commands. But in Azure I have no option for providing npm start.
I have never done such deployment hence I am completely novice.