Why I'm getting error, while trying to redirect requests from nginx to php:apache inside docker containers?

So, in my build, I have three containers - one for db, second one is php-apache for displaying dynamic content, and third is nginx for displaying static content and redirecting dynamic requests to the apache container. Here is my code: docker-compose.yml

version: "3.8"
services:
    db:
        image: "mysql:latest"
        command: --default-authentication-plugin=mysql_native_password
        restart: always
        environment:
          MYSQL_ROOT_PASSWORD: 1
        volumes:
          - ./mysql:/docker-entrypoint-initdb.d
        ports:
          - "3306"
    apache:
        build:
            context: ./apache
        volumes:
          - ./php/dynamic:/var/www/html/
        ports:
            - 81:80
    nginx:
        build:
            context: ./nginx
        ports:
            - 82:80
        volumes:
          - ./php/static:/var/www/html/
        links:
            - apache

Here is my nginx.conf file, which I'm putting inside the container.

server {
    listen 0.0.0.0:80;
    root /var/www/html;
    location / {
        index index.php index.html;
    }
    location ~ \.php$ {
        include fastcgi_params;
        fastcgi_pass apache:81;
        fastcgi_index index.php;
        fastcgi_param SCRIPT_FILENAME $document_root/$fastcgi_script_name;
    }
}

While trying to test web socket, by connecting to the: http://localhost:82/dynamic1.php I'm getting bad gateway error, and in console:

[error] 30#30: *1 connect() failed (111: Connection refused) while connecting to upstream, client: 172.20.0.1, server: , request: "GET /dynamic1.php HTTP/1.1", upstream: "fastcgi://172.20.0.2:81", host: "localhost:82"