The customer authorization (provided in the link you clicked) is out of date, and does not entitle you to use the Blended Threat service.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/exporting-and-importing-fish-if-theres-no-brexit-deal?utm_source=c1b24b61-edde-42e9-b000-cccf947ff3df&utm_medium=email&utm_campaign=govuk-notifications&utm_content=immediate