How to trigger a pipeline once the code is meged and approved in gitlab?

Question

How do we trigger a pipeline in gitlab once the PR is merged and approved. Below is my code:

contactcreate-tst2-19:
  stage: deploy
  script:
    - 'curl --request POST --form token=<token> --form ref=19.0 --form variables[ENVIRONMENT]=TST2 https://vcs.build.livevox.net/api/v4/<id>/trigger/pipeline'
  rules:
    - if: $CI_MERGE_REQUEST_APPROVED
      changes:
        - 'contact/contact-create/TST2/config.json'

anothe rule for below comment question

rules:
    - if: $CI_MERGE_REQUEST_APPROVED
      changes:
        - 'scripter/TST2/scripterTestData.json'
        - 'scripter/.gitlab-scripter.yml'
      when: manual