title: Buildpack error when proper buildpack is already installed
body: <p>I'm trying to Deploy to heroku on my django app, but I'm receiving an error saying:</p>
  <pre><code>remote: -----&gt; App not compatible with buildpack: https://buildpack-registry.s3.amazonaws.com/buildpacks/heroku/python.tgz
  remote:        More info: https://devcenter.heroku.com/articles/buildpacks#detection-failure
  </code></pre>
  <p>however I'm running the correct build pack as far as I can see:</p>
  <pre><code>(virtual) MacBook-Pro-de-Stephen:src stephenlang$ heroku buildpacks
  === programatic-learning Buildpack URL
  heroku/python
  </code></pre>
  <p>Could it be the way I have my files structured?</p>
  <p><a href="https://i.stack.imgur.com/ijFlI.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/ijFlI.png" alt="enter image description here" /></a></p>
  <p>Procfile:
  web: gunicorn blog.wsgi --log-file -</p>
  <p>runtime.txt:
  python-3.8.5</p>
  <p>Is there something I'm missing with regards to deployment?</p>