Problem activating MetaBox with Composer

We followed the tip given to us to use Composer to activate MetaBox using a composer.json file.

Our first problem with this approach was that the key gets exposed within the json file.

And now we do not seem to get MetaBox activated with composer anymore. We tried refreshing the key, and even that did not solve it.

Here is an example of the json we are using:

{
    "name": "x",
    "type": "project",
    "authors": [
        {
            "name": "x",
            "homepage": "https://github.com/y"
        }
    ],
    "minimum-stability": "stable",
    "require-dev": {
        "overtrue/phplint": "^4.0"
    },
    "repositories": [{
        "type": "composer",
        "url": "https://packages.metabox.io/{{OUR KEY}}"
      }],
      "require": {
        "wpmetabox/meta-box": "^5",
        "meta-box/meta-box-aio": "dev-master"
      },
    "config": {
        "allow-plugins": {
            "composer/installers": true
        }
    }
}

Any ideas of what we might be missing?