Docker containers cant communicate (Docker compose / React / NodeJs / Nginx) - node.js

Question

My client isn't able to send requests to backend because it can't resolve the host. I'm trying to pass down the container connection info via an environment variable and use it in the client to connect. However, it is unable to do the requests at all. Any help? Nginx works fine for the frontend part but doesn't work for proxying the backend.
docker-compose.yml
version: '3.2'
services:
server:
restart: always
build:
dockerfile: Dockerfile
context: ./nginx
depends_on:
- backend
- frontend
- database
ports:
- '5000:80'
database:
image: postgres:latest
container_name: database
ports:
- "5432:5432"
restart: always
hostname: database
expose:
- 5432
backend:
build:
context: ./backend
dockerfile: ./Dockerfile
image: kalendae_backend:latest
hostname: backend
container_name: backend
ports:
- "5051:5051"
environment:
- WAIT_HOSTS=database:5432
- DATABASE_HOST=database
- DATABASE_PORT=5432
- PORT=5051
links:
- database
expose:
- 5051
frontend:
build:
context: ./frontend
dockerfile: ./Dockerfile
image: kalendae_frontend:latest
ports:
- "5050:5050"
hostname: frontend
container_name: frontend
environment:
- WAIT_HOSTS=backend:5051
- REACT_APP_BACKEND_HOST=backend
- REACT_APP_BACKEND_PORT=5051
links:
- backend
expose:
- 5050
Nginx config
upstream frontend {
server frontend:5050;
}
upstream backend {
server backend:5051;
}
upstream server {
server server:5000;
}
server {
listen 80;
location / {
proxy_pass http://frontend;
}
location backend {
proxy_pass http://backend;
}
location /backend {
proxy_pass http://backend;
}
}