App platform - TCP communication between services

Hello, I’m creating architecture where I have one main REST API and few microservices that are doing “hard work” behind the scenes.

On my local environment everything works perfectly, but when I try to set up same architecture on digitalocean apps I get Error: connect ECONNREFUSED

My app spec looks like this:

services:
- build_command: npm run build
  environment_slug: node-js
  gitlab:
    branch: develop
    deploy_on_push: true
    repo: html-pdf/html-pdf-api
  http_port: 8080
  instance_count: 1
  instance_size_slug: basic-xxs
  name: dev-html-pdf-api
  routes:
  - path: /
  run_command: npm run start:prod
  source_dir: /
- dockerfile_path: Dockerfile
  gitlab:
    branch: develop
    deploy_on_push: true
    repo: html-pdf/html-pdf-microservice
  http_port: 8080
  instance_count: 1
  instance_size_slug: basic-xxs
  internal_ports:
  - 3000
  name: dev-html-pdf-microservice
  routes:
  - path: /microservice
  run_command: npm run start:prod
  source_dir: /

so as you can see I’ve enabled 3000 internal port.

About the code, microservice is set up to listen on localhost:3000, and the main api is connecting to it using options:

options: {
          host: 'dev-html-pdf-microservice',
          port: 3000,
        }

Unfortunately I get Error: connect ECONNREFUSED 10.245.138.142:3000. I’ve tried many other options with different options on api and microservice but same result.