Gitlab Pipeline Only Merge Request

I'm creating a script for CI in GitLab , but when using only merge_requests it does not run when I create a new merge request .

The version I am using is the Community Edition .

When I create a new branch , a new tag, or commit , GitLab pipeline , it is not firing when I create a new merge request

Can it be something related because I'm using the CE version?

stages:
  - build
  - test
  - deploy

build:
  stage: build
  script: 'echo build'
  only:
  - branches
  - tags
  - merge_requests

test:
  stage: test
  script: 'echo test'
  only:
  - merge_requests

deploy:
  stage: deploy
  script: 'echo deploy'