GitLab-CE 13.7.4: NPM publish 404 Not Found - PUT

Question

I am trying to publish a private NPM package on a self-hosted GitLab. To do this, I created a GitLab project having ID = 9, to host all the NPM packages that I need.

The package.json of the lib is:

{
  "name": "@myscope/api-client",
  "version": "1.0.0",
  ...
  ...
  ...
  "publishConfig":{
    "@myscope:registry": "https://gitlab.mydomain.eu/api/v4/projects/9/packages/npm/"
  }
}

and the following is the .npmrc file:

@myscope:registry=https://gitlab.mydomain.eu/api/v4/packages/npm/
//gitlab.mydomain.eu/api/v4/packages/npm/:_authToken=${GITLAB_AUTH_TOKEN}
//gitlab.mydomain.eu/api/v4/projects/9/packages/npm/:_authToken=${GITLAB_AUTH_TOKEN}

Considering the online documentation I'm not getting what's missing. However, when running the npm publish command I get a 404 Not Found - PUT error. The provided access token has all permissions just to exclude this possibility.

$ GITLAB_AUTH_TOKEN=MyAccessToken npm publish dist
...
...
...
npm ERR! code E404
npm ERR! 404 Not Found - PUT https://gitlab.mydomain.eu/api/v4/packages/npm/@myscope%2fapi-client
npm ERR! 404 
npm ERR! 404  '@myscope/api-client@1.0.0' is not in the npm registry.
npm ERR! 404 You should bug the author to publish it (or use the name yourself!)
npm ERR! 404 
npm ERR! 404 Note that you can also install from a
npm ERR! 404 tarball, folder, http url, or git url.

UPDATE I did also try with the following .npmrc without success, based on the doc at https://docs.gitlab.com/ee/user/packages/npm_registry/index.html#authenticate-with-a-ci-job-token.

@myscope:registry=https://gitlab.mydomain.eu/api/v4/projects/9/packages/npm/
//gitlab.mydomain.eu/api/v4/projects/9/packages/npm/:_authToken=${GITLAB_AUTH_TOKEN}