The customer authorization (provided in the link you clicked) is out of date, and does not entitle you to use the Blended Threat service.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/catch-certificates-for-non-eu-imports-and-exports-of-fish?utm_source=bd28f8ae-2b4d-44aa-9d0c-9371718c72ec&utm_medium=email&utm_campaign=govuk-notifications&utm_content=immediate