The customer authorization (provided in the link you clicked) is out of date, and does not entitle you to use the Blended Threat service.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-after-brexit?utm_source=340f37cd-02d9-4bf5-b983-334b4bee08b8&utm_medium=email&utm_campaign=govuk-notifications&utm_content=immediate