The customer authorization (provided in the link you clicked) is out of date, and does not entitle you to use the Blended Threat service.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/foreign-travel-insurance?utm_source=3c04fac5-b05a-4de7-ae07-2aefd9277b83&utm_medium=email&utm_campaign=govuk-notifications&utm_content=immediate