The customer authorization (provided in the link you clicked) is out of date, and does not entitle you to use the Blended Threat service.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/c041fbbc8d8c5ed3550eb0c9c76c176e?link=https%3A%2F%2Fcommittees.parliament.uk%2Fwork%2F330%2Fmanagement-of-tax-reliefs%2F