The customer authorization (provided in the link you clicked) is out of date, and does not entitle you to use the Blended Threat service.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/export-agricultural-machinery-special-rules?utm_source=168c0fa6-b6a2-4a2c-a00c-9bfa5b61e94e&utm_medium=email&utm_campaign=govuk-notifications&utm_content=immediate