how to set run nginx config for running two frontend apps and a backend server – Docker

I was trying to setup two frontend react applications sharing a server written in nodejs. I tried setting up one frontend application it worked correctly but gets an error host not found in upstream "server" in /etc/nginx/conf.d/default.conf when i add the other one.

here is my docker-compose

version: "3"
services:
  postgres:
    image: "postgres:latest"
    environment:
      - POSTGRES_PASSWORD=postgres_password
  nginx:
    depends_on:
      - api
      - client
      - client2
    restart: always
    build:
      dockerfile: Dockerfile.dev
      context: ./nginx
    ports:
      - "3050:80"
  api:
    build:
      dockerfile: Dockerfile.dev
      context: "./server"
    volumes:
      - /app/node_modules
      - ./server:/app
    environment:
      - PGUSER=postgres
      - PGHOST=postgres
      - PGDATABASE=postgres
      - PGPASSWORD=postgres_password
      - PGPORT=5432
  client:
    stdin_open: true
    environment:
      - CHOKIDAR_USEPOLLING=true
    build:
      dockerfile: Dockerfile.dev
      context: ./client
    volumes:
      - /app/node_modules
      - ./client:/app
  client2:
    stdin_open: true
    environment:
      - CHOKIDAR_USEPOLLING=true
    build:
      dockerfile: Dockerfile.dev
      context: ./client2
    volumes:
      - /app/node_modules
      - ./client2:/app

nginx default.conf

upstream client {
    server client:3000;
}

upstream client2 {
    server client:3000;
}

upstream api {
    server api:5000;
}

server {
    listen 80;

    location / {
        proxy_pass http://client;
    }

    location /login {
        proxy_pass http://client2;
    }

    location /sockjs-node {
        proxy_pass http://client;
        proxy_http_version 1.1;
        proxy_set_header Upgrade $http_upgrade;
        proxy_set_header Connection "Upgrade";
    }

    location /api {
        rewrite /api/(.*) /$1 break;
        proxy_pass http://api;
    }
}

apart from the above my two frontend react applications (client, client2) also contains an nginx directory with default.conf
client/nginx/default.conf

server{
    listen 3000;

    location / {
        root /usr/share/nginx/html;
        index index.html index.htm;
        try_files $uri $uri/ /index.html;
    }
}

client2/nginx/default.conf

one of my client Dockerfile.dev

FROM node:14.14.0-alpine
WORKDIR /app
COPY ./package.json ./
RUN npm i
COPY . .
CMD ["npm", "run", "start"]

one of my client Dockerfile

FROM node:14.14.0-alpine as builder
WORKDIR /app
COPY ./package.json ./
RUN npm i
COPY . .
RUN npm run build

FROM nginx
EXPOSE 3000
COPY ./nginx/default.conf /etc/nginx/conf.d/default.conf
COPY --from=builder /app/build /usr/share/nginx/html