Docker. Can't open file '/app/manage.py?

Question

Docker

backend_1  | python: can't open file '/app/manage.py': [Errno 2] No such file or directory

docker-compose.yml:

version: "3.8"
services:
  backend:
    build:
      context: .
      dockerfile: Dockerfile
    ports:
      - 8001:5000
    volumes:
      - .:/app
    depends_on:
      - db
  db:
    image: mysql:5.7.22
    restart: always
    environment:
      MYSQL_DATABASE: main
      MYSQL_USER: root
      MYSQL_PASSWORD: root
      MYSQL_ROOT_PASSWORD: root
    volumes:
      - .dbdata:/var/lib/mysql
    ports:
      - 33067:3306

Dockerfile:

FROM python:3.9
ENV PYTHONUNBUFFERED 1
WORKDIR /app
COPY requirements.txt /app/requirements.txt
RUN pip install -r requirements.txt
COPY . /app
CMD python main.py

why is it asking for manage.py??