title: __call__() missing 1 required positional argument: 'send' FastAPI on App Engine
body: <p>When trying to host an API on App Engine, the following error keeps coming up. The program used to run on Flask which was working but very slow.</p>
  <h2>Error:</h2>
  <pre><code>&quot;Traceback (most recent call last):
    File &quot;/env/lib/python3.7/site-packages/gunicorn/workers/sync.py&quot;, line 134, in handle
      self.handle_request(listener, req, client, addr)
    File &quot;/env/lib/python3.7/site-packages/gunicorn/workers/sync.py&quot;, line 175, in handle_request
      respiter = self.wsgi(environ, resp.start_response)
  TypeError: __call__() missing 1 required positional argument: 'send'
  &quot;
  </code></pre>
  <h2>Docker File:</h2>
  <pre><code>FROM gcr.io/google_appengine/python
  
  RUN apt-get update &amp;&amp; apt-get install -y ffmpeg
  
  # Create a virtualenv for dependencies. This isolates these packages from
  # system-level packages.
  
  RUN virtualenv /env -p python3.7
  
  # Setting these environment variables are the same as running
  # source /env/bin/activate.
  
  ENV VIRTUAL_ENV /env
  ENV PATH /env/bin:$PATH
  
  ADD requirements.txt /app/requirements.txt
  RUN pip install -r /app/requirements.txt
  
  # Add the application source code.
  
  ADD . /app
  
  CMD gunicorn -w 4 -k uvicorn.workers.UvicornWorker main:app
  </code></pre>
  <h2>app.yaml</h2>
  <pre><code>runtime: custom
  env: flex
  entrypoint: gunicorn -w 4 -k uvicorn.workers.UvicornWorker main:app
  service: encoder
  
  runtime_config:
    python_version: 3
  
  handlers:
  
  - url: /.*
    script: auto
  </code></pre>