Not able to deploy heroku app even with valid API keys and secret

[avaiyahardik]

I am trying to deploy this heroku app with valid google / twilio API keys and secrets, however, it is failing to deploy.

Given below error during Build app:

There was an issue building your app. This can mean your app.json's project is not a valid Heroku application. Please ensure your app is deployable to Heroku and try again.

-----> Building on the Heroku-20 stack
-----> Determining which buildpack to use for this app
-----> Python app detected
-----> Using Python version specified in runtime.txt
! Requested runtime (python-3.6.5) is not available for this stack (heroku-20).
! Aborting. More info: https://devcenter.heroku.com/articles/python-support
! Push rejected, failed to compile Python app.
! Push failed

I appreciate your work.