Have you ensured that the /api/atelier/ web application  has the %Developer role assigned, this caught me out initially.

More info here: https://docs.intersystems.com/atelier/latest/index.jsp

OK so I have now got this working after a lot of googling etc.  In the registry at Computer\HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Internet Explorer\Main\FeatureControl\FEATURE_BROWSER_EMULATION ensure you have a REG_DWORD entry for eclipse.exe with a  Decimal value of 11001

Hopefully this should help anyone facing this issue.