CORS Error From Docker Flask Container

Hello, I currently have a Flask/React App that I am using in tandem with Docker. I wrote Dockerfiles for both the backend (Flask) and frontend (React), and a docker-compose.yml to combine the two together and initialize my app when I use the command “docker-compose up”.

I am able to start the app correctly, but when I try to login and send the api request to the backend, I am presented with the following CORS error:

Access to XMLHttpRequest at 'http://127.0.0.1:5000/login' from origin 'http://localhost:3000' has been blocked by CORS policy: Response to preflight request doesn't pass access control check: No 'Access-Control-Allow-Origin' header is present on the requested resource.

I am not having this error in my application when run out of the containers, so I am pretty positive it is related to the configuration of the Dockerfiles/ports. Here are my Dockerfiles and the docker-compose.yml. I know my flask app itself is configured with CORS to avoid this error when the app is not run in the container.

Backend

FROM python:3

WORKDIR /app

ENV FLASK_APP=main.py

COPY ./requirements.txt .

RUN pip install -r requirements.txt

COPY . .

CMD ["python", "main.py"]

Frontend

FROM node:14-slim

WORKDIR /user/src/app

COPY ./package.json ./
COPY ./package-lock.json ./

RUN npm install

COPY . .

EXPOSE 3000

CMD ["npm", "start"]

Docker-Compose

version: "3.9"
services:
  server:
    build: ./backend
    ports:
    - "80:5000"
    volumes:
    - ./backend:/app
    environment:
      FLASK_ENV: development
  web:
    build: ./frontend
    ports:
      - "3000:3000"
    volumes:
      - ./frontend:/user/src/app
    depends_on:
      - server

Below is the partial frontend JavaScript function that handles the data being sent to the backend:

const handleSubmit = async (event) => {
    try {
      event.preventDefault()
      const payload = {name:username, password:password}
      const response = await axios.post("http://127.0.0.1:5000/login", payload, {headers:{
        'Access-Control-Allow-Origin' : '*',
        'Content-Type': 'application/json'
    }})

Any folks out there have encountered a similar issue and may have potential recommendations?