[Python] Trouble setting PORT in Django/Heroku Procfile using Waitress

I'm trying to deploy my Django application with Heroku (on Windows), and using Waitress (because Gunicorn no longer runs on Windows??). When I hard coded the PORT number, I was able to run it fine.

When I try to define PORT in the Procfile as an environment variable

Procfile:

web: waitress-serve --port=$PORT [projectname].wsgi:application


from .env

WEB_CONCURRENCY=2
PORT=$PORT


from settings.py

import environ
from environ import Env
env = Env()
...
PORT = env('PORT')


running "heroku local" produces

ValueError: invalid literal for int() with base 10: '$PORT'


Ultimately I'm trying to resolve a failure to bind to PORT:

Error R10 (Boot timeout) -> Web process failed to bind to $PORT `within 60 seconds of launch`


I keep seeing mention that "$PORT" is not appropriate for Windows. However I can't figure out what I'm missing. I've seen suggestions that "%PORT%" would work for Windows, but I haven't had success. I've also tried "PORT" without symbols (as the Waitress docs seem to suggest). If there is a Windows friendly syntax, would I need to use it in both .env and Procfile?

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