The customer authorization (provided in the link you clicked) is out of date, and does not entitle you to use the Blended Threat service.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-uks-trade-agreements?utm_source=2a8c9e9d-d955-4727-bb9c-da93dc3e61c5&utm_medium=email&utm_campaign=govuk-notifications&utm_content=immediate