React App as a Django App in a Docker Container - connection refused when trying to access APIs on localhost:8000 urls - reactjs

Question

hope you might have some guidance for me on this.
Right now I have a React app that is part of a Django app (for the sake of ease of passing auth login tokens), which is now containerised in a single Dockerfile. Everything works as intended when it is run as a Docker instance locally, but the Docker Image is having issues, despite the fact that the webpages are visible when the Image is deployed on server.
Specifically, when the Docker image is accessed, the home page renders as expected, but then a number of fetch requests which usually go to localhost:8000/<path>/<to>/<url> return the following error:
GET http://localhost:8000/<path>/<to>/<url> net::ERR_CONNECTION_REFUSED
On a colleague's suggestion, I have tried changing localhost:8000 to the public IP address of the server the Docker Image is hosted on (eg 172.XX.XX.XXX:8000) but when I rebuild the React app, these changes do not remain, and it defaults back to localhost. Here are my questions:
Is this something I change from within the React application itself? Do I need manually assign an IP address? (This seems unlikely to me)
Or is this something to do with either the Django port settings, or the Dockerfile itself?
Here is the Dockerfile
FROM ubuntu:18.04
# ...
RUN apt-get update && apt-get install -y \
software-properties-common
RUN add-apt-repository ppa:deadsnakes/ppa
RUN apt-get update && apt-get install -y \
python3.7 \
python3-pip
RUN python3.7 -m pip install pip
RUN apt-get update && apt-get install -y \
python3-distutils \
python3-setuptools
RUN python3.7 -m pip install pip --upgrade pip
# ???
ENV PYTHONUNBUFFERD 1
# copy file form local machine to container
COPY ./requirement.txt /requirement.txt
# install dependency
# RUN pip install -r /requirement.txt
RUN pip install -r /requirement.txt
# create app folder in container
RUN mkdir /app
# set default working dictionary
WORKDIR /app
# copy local app folder to container folder
COPY ./app /app
CMD ["python", "test.py"]
Multiple technologies, multiple failure points - thanks in advance!