secure.gateway.gov.uk
The Government Gateway developed in 2002 is nearing end of life and will be decommissioned on 14th February 2018. It will not be able to accept submissions (e.g. RTI FPS) from this date.
They have developed a new version for Document submission via a new transaction engine, available at a new URL:
https://transaction-engine.tax.service.gov.uk
Cleanlink Site Manager v6.07 implements this URL change.