Multi-project pipeline with trigger , example from the gitlab docs doesn't work

The example for the multi project pipeline with mirroring status ( https://docs.gitlab.com/ee/ci/multi_project_pipelines.html#mirroring-status-from-triggered-pipeline) doesn't work:

trigger_job:
  trigger:
    project: my/project
    strategy: depend

Leads to an error: "This GitLab CI configuration is invalid: jobs:trigger_pipeline_in_another_repo config contains unknown keys: trigger"

config:

trigger_pipeline_in_another_repo:
  stage: trigger_pipeline_in_b
  script:
    - apt-get update && apt-get upgrade -y
    - apt-get install curl -y
    - curl --request POST --form "token=$CI_JOB_TOKEN" --form ref=master http://35.184.231.241/api/v4/projects/8/trigger/pipeline
  trigger:
    project: root/isolated_pipeline
    strategy: depend