At the Application Profile Overview of the datacite schema https://guidelines-other-products.readthedocs.io/en/latest/application_profile.html
the url to the Datacite portal http://datacite.org/schema/kernel-4 is an XML Namespace and should not have a link and should not be clickable since it has no landing page available.
Additionally, the mentioned guideline page is for "Guidelines for Other Research products" but has the title of Guidelines for Software Repository managers