FastAPi and ReactJS app configuration on EC2

I have a FastAPI backend app running on venv in an EC2 machine AND my ReactJS frontend app is on the SAME Ubuntu EC2machine. Both are running successfully.

My ReactJS frontend app is accessible via the Nginx pointing to my EC2 public IPv4 address. However, i need the ReactJS app to call the FastAPI local endpoint (127.0.0.1:8000 or localhost:8000 ?). Perhaps there's a port/configuration step i'm missing.

Note, this all worked locally on a PC, i've just ported this to EC2.