Gitlab CI: why do I get an error when I try to define the pages stage?

I’m trying to publish a create-react-app on Gitlab, using its CI.

This is my .gitlab-ci.yml file:

stages:
  - build
  - pages

build:
  image: node:16
  stage: build
  script:
    - npm install
    - npm build
  artifacts:
    paths:
      - build/

pages:
  image: alpine:latest
  stage: deploy
  variables:
    GIT_STRATEGY: none        # Do not clone git repo
  script:
    - mv build public         
  artifacts:
    paths:
      - public  
  rules:
    - if: $CI_COMMIT_BRANCH == $CI_DEFAULT_BRANCH

But unfortunately I get this error:

This GitLab CI configuration is invalid: pages job: chosen stage does not exist; available stages are .pre, build, pages, .post.

What’s wrong with my configuration?

>Solution :

You need to change your stages.

You have:

stages:
  - build
  - pages

but define:

pages:
  image: alpine:latest
  stage: deploy

The stage needs to match:

stages:
  - build
  - deploy <-------