The customer authorization (provided in the link you clicked) is out of date, and does not entitle you to use the Blended Threat service.
https://www.gov.uk/government/collections/the-media-and-broadcasting-sectors-from-january-2021?utm_source=5b9fa1f7-e8af-48fb-8098-f953cd433c27&utm_medium=email&utm_campaign=govuk-notifications&utm_content=daily