The customer authorization (provided in the link you clicked) is out of date, and does not entitle you to use the Blended Threat service.
http://www.acumen.hmrc.gov.uk/_/app/emailRobot/index/click/secret/9c85629291a5c6c8c84dbc3e1c4e1af4?link=https%3A%2F%2Fwww.gov.uk%2Fhmrc-internal-manuals%2Fappeals-reviews-and-tribunals-guidance