Connection refused on connecting to container in gitlab

GitLab CI/CD
1

I am trying to create a write a step to verify pacts to a provider via below in gitlab.yml:

imaging:
  stage: imaging
  image:
    name: gcr.io/kaniko-project/executor:debug
    entrypoint: [""]
  script:
    - echo "{\"auths\":{\"$CI_REGISTRY\":{\"username\":\"$CI_REGISTRY_USER\",\"password\":\"$CI_REGISTRY_PASSWORD\"}}}" > /kaniko/.docker/config.json
    - /kaniko/executor --context $CI_PROJECT_DIR --dockerfile $CI_PROJECT_DIR/Dockerfile --destination $CI_REGISTRY_IMAGE:$CI_COMMIT_SHORT_SHA --destination $CI_REGISTRY_IMAGE:$CI_COMMIT_REF_SLUG


pact-provider-verification:
  stage: pact-provider-verification
  image:
    name: pactfoundation/pact-cli:latest
    entrypoint: [""]
  services:
    - name: ${CI_REGISTRY_IMAGE}:${CI_COMMIT_SHORT_SHA}
      alias: app
  script:
    - "pact verify 
      --consumer-version-tag=master 
      --provider=pact-provider 
      --provider-app-version=$CI_COMMIT_SHORT_SHA 
      --provider-version-tag=$CI_COMMIT_REF_NAME 
      --provider_base_url=http://app:8000
      --provider-states-setup-url=http://app:8000/provider-states 
      --pact-broker-base-url=$PACT_BROKER_BASE_URL 
      --broker-token=$PACT_BROKER_TOKEN 
      --wait=10 
      --publish-verification-results"

but I’m getting an error: Connection refused - connect(2) for "app" port 8000)

docker-compose.yml:

services:
  app:
    image: pact-provider:latest
    ports:
      - "8081:8081"