MTD VAT
Reconnecting MTD for VAT when the link drops
Expired OAuth tokens, revoked grants, and how to re-authorise a client safely.
MTD links can expire or be revoked from the Government Gateway. Open the client workspace and use Connect HMRC (or reconnect) to run OAuth again.
If credentials were rotated on the Developer Hub, update environment variables and restart — never mix test and live secrets.
A credential problem looks different from a validation error: reconnect first, then retry the return.