The customer authorization (provided in the link you clicked) is out of date, and does not entitle you to use the Blended Threat service.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/claim-vat-refunds-from-eu-countries-from-1-january-2021?utm_source=ae48968b-4fa3-41f8-a2d9-c18ebd7ad718&utm_medium=email&utm_campaign=govuk-notifications&utm_content=daily