The customer authorization (provided in the link you clicked) is out of date, and does not entitle you to use the Blended Threat service.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/list-of-customs-agents-and-fast-parcel-operators?utm_source=1f89beda-0aec-474c-af0e-8a47637a9f7d&utm_medium=email&utm_campaign=govuk-notifications&utm_content=immediate