HMRC connection
Fraud-prevention headers — why submit can be blocked
Hydra refuses to call MTD APIs when browser metadata is incomplete.
UK law requires fraud-prevention headers on MTD VAT and Income Tax calls. Hydra collects fresh browser metadata at submit time — never from a stale cache.
If anything is missing (timezone, screen metrics, local IPs, vendor fields), the request is blocked locally with a clear error before it reaches HMRC.
Retry from a normal browser session; embedded previews or locked-down environments that hide device signals may need a full desktop browser.