The customer authorization (provided in the link you clicked) is out of date, and does not entitle you to use the Blended Threat service.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/trusts-and-capital-gains-tax?utm_source=aa160198-0156-4033-8703-cad5f8a5d342&utm_medium=email&utm_campaign=govuk-notifications&utm_content=immediate