The customer authorization (provided in the link you clicked) is out of date, and does not entitle you to use the Blended Threat service.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/guidance/register-your-clients-trust?utm_source=1208d7d8-dc22-44de-a34c-e2b11142f401&utm_medium=email&utm_campaign=govuk-notifications&utm_content=immediate