Connect to Mysql database from another docker application

I have 2 Laravel applications running in docker environment.

The first application docker-compose file (which called mobile app)

version: '3.8'

networks:
    laravel:

services:
    nginx:
        build:
            context: .
            dockerfile: dockers/nginx/Dockerfile
        container_name: mobile-server-nginx
        ports:
            - "8188:80"
        volumes:
            - ./:/var/www/
        depends_on:
            - php
            - mysql
        networks:
            - laravel
    mysql:
        image: mysql:8.0.28
        container_name: mobile-server-mysql
        tty: true
        ports:
            - "5306:3306"
        volumes:
            - ./mysql:/var/lib/mysql
        environment:
            MYSQL_DATABASE: ${DB_DATABASE}
            MYSQL_USER: ${DB_USERNAME}
            MYSQL_PASSWORD: ${DB_PASSWORD}
            MYSQL_ROOT_PASSWORD: ${DB_ROOT_PASSWORD}
            SERVICE_TAGS: dev
            SERVICE_NAME: mysql
        networks:
            - laravel
    php:
        build:
            context: .
            dockerfile: dockers/php/Dockerfile
        container_name: mobile-server-php
        extra_hosts: 
            - "host.docker.internal:host-gateway"
        volumes:
            - ./:/var/www/
        ports:
            - "9001:9000"
        networks:
            - laravel
        depends_on:
            - mysql

The second application docker-compose file: (which called resident app)

version: '3.7'

networks:
    resident:

services:
    nginx:
        build:
            context: .
            dockerfile: dockers/nginx/Dockerfile
        container_name: resident-backend-nginx
        ports:
            - "8088:80"
        volumes:
            - ./:/var/www/
        depends_on:
            - php
            - mysql
        networks:
            - resident
    mysql:
        image: mysql:5.7.22
        container_name: resident-backend-mysql
        tty: true
        ports:
            - "6306:3306"
        volumes:
            - ./mysql:/var/lib/mysql
        environment:
            MYSQL_DATABASE: ${DB_DATABASE}
            MYSQL_USER: ${DB_USERNAME}
            MYSQL_PASSWORD: ${DB_PASSWORD}
            MYSQL_ROOT_PASSWORD: ${DB_ROOT_PASSWORD}
            SERVICE_TAGS: dev
            SERVICE_NAME: mysql
        networks:
            - resident
    php:
        build:
            context: .
            dockerfile: dockers/php/Dockerfile
        container_name: resident-backend-php
        extra_hosts: 
            - "host.docker.internal:host-gateway"
        volumes:
            - ./:/var/www/
        ports:
            - "9002:9000"
        networks:
            - resident
        depends_on:
            - mysql

2 applications work separated perfectly. Now, in mobile application, I want to connect to resident application database to retrieve some data.
In the mobile application:

• In config/database.php, I added 1 more database connection:

        'resident_mysql' => [
            'driver' => 'mysql',
            'url' => env('DATABASE_RESIDENT_URL'),
            'host' => env('DB_RESIDENT_HOST', '127.0.0.1'),
            'port' => env('DB_RESIDENT_PORT', '3306'),
            'database' => env('DB_RESIDENT_DATABASE', 'forge'),
            'username' => env('DB_RESIDENT_USERNAME', 'forge'),
            'password' => env('DB_RESIDENT_PASSWORD', ''),
            'unix_socket' => env('DB_RESIDENT_SOCKET', ''),
            'charset' => 'utf8mb4',
            'collation' => 'utf8mb4_unicode_ci',
            'prefix' => '',
            'prefix_indexes' => true,
            'strict' => true,
            'engine' => null,
            'options' => extension_loaded('pdo_mysql') ? array_filter([
                PDO::MYSQL_ATTR_SSL_CA => env('MYSQL_ATTR_SSL_CA'),
            ]) : [],
        ],

• Then, I set env variables in .env file:

DB_RESIDENT_HOST=127.0.0.1
DB_RESIDENT_PORT=6306 // exposed mysql port in `resident_app`
DB_RESIDENT_DATABASE={database name}
DB_RESIDENT_USERNAME={database_user}
DB_RESIDENT_PASSWORD={database_password}

• Create an api to test in api.php:

Route::get('test', function () {
    $user = DB::connection('resident_mysql')->select('select * from users');
    return $user;
});

• Finally, test api with postman, but it shows error SQLSTATE[HY000] [2002] Connection refused (SQL: select * from users)
  

I’ve searched for this error but cannot find any answer.

UPDATE

• According from @David Maze, I’ve changed some config in docker-compose file in mobile app.
• In docker-compose file, add external network

networks:
    laravel:
        driver: bridge
    residentbackend_resident: // this is network in `resident` app, which type is `bridge`
        external: true

• Then add external network to php service in networks section:

        networks:
            - laravel
            - residentbackend_resident

• In .env, change DATABASE_HOST to mysql service name of resident app

DB_RESIDENT_HOST=mysql1

But it still return the same error as above.